Jami` at-Tirmidhi 300
جامع الترمذي#300SahihThawban, the freed slave of Allah's Messenger, narrated that :Allah's Messenger said: "When Allah's Messenger wanted to turn from his Salat, he would seek forgiveness from Allah three times, then say: (Allahumma Antas-Salam, wa minkas-salam, tabarakta ya dhal-jalali wal-Ikram) 'O Allah! You are the One free of defects and perfection is from You. Blessed are You, O Possesor of Majesty and Honor
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Ahmad Muhammad ShakirSahih
Al-AlbaniSahih
Bashar Awad MaaroufHasan Sahih
Zubair Ali ZaiSahih Muslim
In-book reference: 2:152