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I guess by "Barath fasting" you mean 15th of Shaban. Below is a response from askimam.org website

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Virtues of the month of Sha’ban

There are many Ahadeeth regarding the virtues of Sha’ban. Hereunder are a few:
‏عن ‏ ‏عائشة أم المؤمنين ‏ ‏رضي الله عنها ‏ ‏أنها قالت ‏‏كان رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏يصوم حتى نقول لا يفطر ويفطر حتى نقول لا يصوم وما رأيت رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏استكمل صيام شهر قط إلا رمضان وما رأيته في شهر أكثر منه صياما في شعبان

1. Translation: Aisha (Radhiyalahu Anha) reported that the Messenger of Allah (صلى الله عليه وسلم) used to observe fasts (so continuously) that we said that he would not break, and did not observe (them) till we said that he would not fast: and I did not see the Messenger of Allah (صلى الله عليه وسلم) completing the fast of a month, but that of Ramadan, and I did not see him fasting more in any other month than that of Sha’ban. [Sahih Muslim, Chapter 6, Hadith Number 2580]

‏عن ‏ ‏عائشة أم المؤمنين ‏ ‏رضي الله عنها ‏ كان رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏يتحفظ ‏ ‏من شعبان ما لا ‏ ‏يتحفظ ‏ ‏من غيره ثم يصوم لرؤية رمضان فإن ‏ ‏غم عليه ‏ ‏عد ثلاثين يوما ثم صام

2. Translation: Narrated By Aisha (Radhiyallahu Anha) : Rasullullah(صلى الله عليه وسلم) used to count the days in Sha’ban in a manner he did not count any other month; then he fasted when he sighted the new moon of Ramadan; but if the weather was cloudy he counted thirty days and then fasted. [Abu Dawud, Chapter 7, Hadith Number 2318]

‏عن عائشة قالت: لم يكن رسول الله صلى الله عليه وسلم في شهر أكثر صياماً منه في شعبان لأنه ينسخ فيه أرواح الأحياء في الأموات، حتى أن الرجل يتزوج وقد رفع اسمه فيمن يموت، وإن الرجل ليحج وقد رفع اسمه فيمن يموت
3. Translation: Narrated by Aishah (Radhiyallahu Anha) says, “Prophet Muhammad (صلى الله عليه وسلم) used to fast the whole of Sha’ban. I said to him, ‘Messenger of Allah, is Sha’ban your most favorite month for fasting?’ He said, ‘In this month Allah prescribes the list of the persons dying this year. Therefore, I like that my death comes when I am in a state of fasting.” [Ibn Asakir, Tafsir ad-Dar al-Manthur Under the Verse 44:3]
‏عن ‏ ‏عمران بن حصين ‏ ‏رضي الله عنهما ‏‏أن رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏قال له ‏ ‏أو لآخر ‏ ‏أصمت من ‏ ‏سرر ‏ ‏شعبان قال لا قال فإذا أفطرت فصم يومين
4. Translation: Imran bin Husain (Radhiyallahu Anhu) reported that Allah’s Messenger (صلى الله عليه وسلم) having said to him or to someone else: Did you fast in the middle of Sha’ban? He said: No. Thereupon he (the Holy Prophet) said: If you did not observe fast, then you should observe fast for two days. [Muslim, Chapter 6, Number 2607]
Conclusion:
These reports indicate that fasting in the month of Sha`baan, though not obligatory, is so meritorious that the Holy Prophet (صلى الله عليه وسلم) did not like to miss it.
It is the habit of the Muslims to celebrate some auspicious events during the month of Sha’ban by praying, reciting Quran, praising Allah, and making a great deal of supplication to Allah during that night. Sha’ban is like an introduction to Ramadan and it has some things in common with Ramadan, such as fasting, reciting Holy Quran and giving in charity. It has been narrated that upon the arrival of Rajab the Holy Prophet (صلى الله عليه وسلم) used to pray “O’ Allah! Bless us abundantly in Rajab and Sha’ban and deliver us safely unto Ramadan.”

Virtues of the 15th night of Sha’ban:

‏عن‏ ‏عائشة ‏ ‏قالت ‏‏فقدت رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏ليلة فخرجت فإذا هو ‏ ‏بالبقيع ‏ ‏فقال ‏ ‏أكنت تخافين أن يحيف الله عليك ورسوله قلت يا رسول الله إني ظننت أنك أتيت بعض نسائك فقال إن الله عز وجل ينزل ليلة النصف من شعبان إلى السماء الدنيا فيغفر لأكثر من عدد شعر غنم ‏ ‏كلب

1. Translation: Narrated by Aisha (Radhiyallahu Anha) I missed Allah’s Messenger (صلى الله عليه وسلم) during the night and found him in al-Baqi’. He said: Were you afraid that Allah and His Messenger would deal unjustly with you? I said: Allah’s Messenger, I thought that you had gone to some of your other wives. He (the Prophet) said: Verily Allah, the Exalted and Glorious, comes down to the heaven of the world in “the middle night of Sha’ban” and forgives sins even more abundant than the hair of the goats of Kalb. [Sunan Tirmidhi ,Volume 1, Hadith Number 670, Ibn Maja, Volume 2, Hadith Number 1379]

عن‏ ‏أبي موسى الأشعري ‏عن رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏قال ‏ ‏إن الله ليطلع في ليلة النصف من شعبان فيغفر لجميع خلقه إلا لمشرك أو مشاحن

2. Translation: Narrated by Abu Musa al-Ash’ari (Radhiyallahu Anha) that Allah’s Messenger (صلى الله عليه وسلم) said, Allah, the Exalted and Glorious looks down on “the middle night of Sha’ban” and forgives all His creation. except a polytheist or one who is mushahin. [Sunan Ibn Maja, Volume 2, Hadith Number 1380]
عن عبد الله بن عمرو بن العاص أن رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏قال ‏ ‏يطلع الله عز وجل إلى خلقه ليلة النصف من شعبان فيغفر لعباده إلا لاثنين ‏مشاحن ‏وقاتل نفس‏

3. Translation: Narrated by Abdullah ibn Amr ibn al-’As that Allah’s Messenger (صلى الله عليه وسلم) said, Allah, the Exalted and Glorious looks down on “the middle night of Sha’ban” and forgives all His creation except two people, the mushahin and the murderer. [Musnad Ahmad, Volume 3, Hadith Number 6353]

عن أبي ثعلبة الخشني، عن النبي صلى الله عليه وسلم قال: إذا كان ليلة النصف من شعبان، اطلع الله تعالى إلى خلقه، فيغفر للمؤمنين، ويملي للكافرين، ويدع أهل الحقد بحقدهم حتى يدعوه

4. Translation: It is related by Abu Thalaba that the Blessed Prophet (صلى الله عليه وسلم) said: On the 15th night of Shabaan, Allah looks over at his creation and forgives all the believers except for the one who begrudges and hates. He leaves them in their enmity. [Bayhqi, Tafsir ad-Dar al-Manthur Under the Verse 44:3]

عن معاذ بن جبل، عن النبي صلى الله عليه وسلم قال: يطلع الله في ليلة النصف من شعبان، فيغفر لجميع خلقه إلا لمشرك أو مشاحن

5. Translation: It is related by Muaz bin Jabbal that the Blessed Prophet (صلى الله عليه وسلم) said: Allah looks at His creation in “the night of mid-Sha`ban” and He forgives all His creation. except for a mushrik (idolater) or a mushahin (one bent on hatred). [Ibn Hibban, Sahih, ed. Shu`ayb Arna'ut Volume 012: Hadith Number 5665]
عن عائشة قالت: قام رسول الله صلى الله عليه وسلم من الليل يصلي، فأطال السجود حتى ظننت أنه قد قبض، فلما رأيت ذلك، قمت حتى حركت إبهامه، فتحرك، فرجعت، فلما رفع رأسه من السجود وفرغ من صلاته، فقال: ” يا عائشة، أو يا حميراء ظننت أن النبي قد خاس بك ” قلت: لا والله يا نبي الله ولكني ظننت أنك قبضت لطول سجودك فقال: ” أتدرين أي ليلة هذه؟ ” قلت: الله ورسوله أعلم، قال: ” هذه ليلة النصف من شعبان، فيغفر للمستغفرين ويرحم المسترحمين ويؤخر أهل الحقد كما هم

6. Translation: From A’isha: She said: The Prophet (صلى الله عليه وسلم) stood up in prayer during part of the night and made his prostration so lengthy that I thought his soul had been taken back. When I saw this I got up and went to move his big toe, whereupon he moved, so I drew back. When he raised his head from prostration and finished praying, he (صلى الله عليه وسلم) said: “O A’isha, O fair little one (humayra’)! Did you think that the Prophet had broken his agreement with you?” She replied: “No, by Allah, O Messenger of Allah, but I thought that your soul had been taken back because your stayed in prostration for so long.” He said: “Do you know what night this is?” She said: “Allah and His Prophet know best.” He said: “This is the night of mid-Sha`ban! Verily Allah the Glorious and Majestic look at His servants on “the night of mid-Sha`ban, and He forgives those who ask forgiveness, and He bestows mercy on those who ask mercy, and He gives a delay to the people of envy and spite in their state.”


‏عن ‏ ‏عمران بن حصين ‏ ‏رضي الله عنهما ‏‏أن رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏قال له ‏ ‏أو لآخر ‏ ‏أصمت من ‏ ‏سرر ‏ ‏شعبان قال لا قال فإذا أفطرت فصم يومين

7. Translation: Imran bin Husain (ra) reported Allah’s Messenger (صلى الله عليه وسلم) having said to him or to someone else: Did you fast in the “Middle of Sha’ban?” He said: No. Thereupon he (the Holy Prophet) said: If you did not observe fast, then you should observe fast for two days. [Muslim, Chapter 6, Number 2607]
And Allah Ta’āla Knows Best
Moulana Ismail Desai,
Student Darul Iftaa
Durban, South Africa
Checked and Approved by,
Mufti Ebrahim Desai. source: http://www.askimam.org/public/question_detail/21318