[PekHyvac]

Salam Aleykum,

Very nice thread Mashallah,

Dua of entering the Masjid:

Arabic:
أَعوذُ باللهِ العَظيـم وَبِوَجْهِـهِ الكَرِيـم وَسُلْطـانِه القَديـم مِنَ الشّيْـطانِ الرَّجـيم Transliteration:
"aAAoothu billahil-AAatheem wabiwajhihil-kareem wasultanihil-qadeem minash-shaytanir-rajeem"

Translation:
"I take refuge with Allah, The Supreme and with His Noble Face, and His eternal authority from the accursed devil."

Source of this Dua from the Sunnah:

لقيت عقبة بن مسلم فقلت له بلغني أنك حدثت عن عبدالله بن عمرو بن العاص أن رسول الله صلى الله عليه وسلم كان يقول إذا دخل المسجدأعوذ بالله العظيم وبوجهه الكريم وسلطانه القديم من الشيطان الرجيم قال اقط قلت نعم قال فإذا قال ذلك قال الشيطان حفظ مني سائر ذلك اليوم Translation: "I met 'Uqbah bin Muslim so I said to him: It had reached me that you have narrated from 'Abdullah ibn 'Amro bin al-'Aas that the Messenger of Allah PBUH used to say as he entered the mosque: [And he mentions the Dua above], He replied: Yes, and if he said these the Shaytan would say: "He is safe from me for the rest of this day."

source: al-Munthiri in his "Al-Targheeb wal-Tarheeb" vol.2 page 380, He said about it:
"لا ينزل عن درجة الحسن وقد يكون على شرط الصحيحين أو أحدهما"
"The rank of this Hadith is no less than 'Hasan' and it could be 'Sahih' on the condition of the two Sheikhs(Bukhari & Muslim) or one of them."

This Hadith seems to be narrated through 'Amro ibn al-'Aas (ra) although I found another through Mu'ath ibn Jabal (ra):

كان رسول الله - صلى الله عليه وسلم - يقول إذا دخل المسجد : أعوذ بالله العظيم ، وبوجهه الكريم ، وسلطانه القديم ، من الشيطان الرجيم ، قال : فإذا قال ذلك ؛ قال الشيطان : حفظ مني سائر اليوم Mu'ath said: The Prophet PBUH used to say as he enters the Masjid: [He mentions the above Dua], he said: If I say it then Shaytan will say: "He is safe from me for the rest of this day."

source: al-Albani in "Takhreej Mishkat al Masabih" #714, He said about it: Isnaduhu Sahih.

Salam Aleykum,