Yes it is sahih and it is AUTHENTIC. Even Shaikh Albani accepts it as Sahih. This is why you should never do things in haste. Always first ask 'Ulama then give a fatwa. Here is the Hadith: This hadeeth is Saheeh (authentic li-ghairihi) and is narrated in Abu Dawood (1297), Ibn Majah (1387) al-Haakim (1-308). Al-Haafidth ibn Hajar said, 'And in the narration of At-Tabrani: even if your sins were as the foam of the sea, or as much as the sand, Allah would forgive you...' Abu Bakr b. Abi Dawood said that he heard his father say, 'There is nothing in the Tasbeeh prayer more authentic than this hadeeth.' Imam Muslim said, 'There is no hadeeth with a better chain of narrators in this matter other than this...' (i.e. Ibn Abbas narration). The second hadeeth, which is also authentic (Saheeh li-ghairihi) is narrated on the authority of Abi Rafi'...it to is similar to the above (in its wording). This narration was narrated by Ibn Majah, at-Tirmidthi, Ad'daar-Qutni, and al-Baihaqi. Al-Baihaqi said, that Abdullah b. al-Mubarak used to pray the Tasbeeh prayer, this prayer was handed (to us) by the pious predecessors, and from this, the above hadeeth gains extra strength...! At-Tirmidthi said, 'this is a ghareeb hadeeth from the narration of Abi Rafi' he then said, 'Ibn al-Mubarak used to practice it, and other people of knowledge used to practice it also, and they mentioned its merits.' Of those who corrected (authenticated) the above hadeeth:- 1. Abu Dawood, 2. Ibn Mundah, 3. Al-Aajari, 4. As-Sum'aani, 5. al-Madini, 6. al-Mundthiri, 7. Abul-Hasan al-Mundthiri, 8. Ibn As-Salaah, 9. Ad-Dailami, 10. Al-Haakim, 11. Al-A'laali, 12. Az-Zurkashi, 13. Al-Muhaamili, 14. Abul-Hasan al-Muqdasi, 15. al-Juwaini, 16. Al-Baghawi, 17. Ar-Ra'fiee', 18. Al-Haitami, 19. As-Su'youti, 20. Al-Luknawwi, 21. Ibn Aa'bideen, 22. Al-Albani and others... Yes you made a mistake. There is no doubt in this one. The question is very general. You need to be specific. In this case, you did not do a good thing by stopping her. The doubt here was just lack of knowledge.