Sayyiduna Ali (may Allah be pleased with him) narrates: The Prophet Muhammad (peace and blessings be upon him) used to recite this at the very end between Tashahhud and Salam: "O Allah! Forgive me for what I have done before and what I will do later, what I have done secretly and what I have done openly, and for any excess, and for everything about which You have more knowledge than I do. O Allah, forgive me for all of that. Surely, You are the One Who brings forward and the One Who delays. There is no deity except You."
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 1966
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صفة الصلاة».فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح، بحر بن نصر: ثقة، ومن فوقه من رجال الشيخين غير يعقوي والد يوسف، فإنه من رجال مسلم.