Sahih al-Bukhari 6328
صحيح البخاري#6328SahihNarrated `Abdullah:We used to say in the prayer: 'AsSalam be on Allah, As-Salam be on so-and-so.' So one day the Prophet said to us, "Allah Himself is As-Salam; when anyone of you sits during his prayer, he should say: 'at-tah, iyyatu-li l-lahi,' up to 'As-Salihin,' (All the compliments are for Allah ...righteous people) for when he recites this, then he says his Salam to all the righteous people present in the heavens and on the earth. Then he should say, 'I testify that none has the right to be worshipped except Allah, and that Muhammad is His slave and His Apostle,' and then he can select whatever he likes to celebrate (Allah's) Praises
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 80:25