question #3 Sahih Muslim 484c, Book 4, Hadith 249 : What is the significance of seeking forgiveness in the prayers of the Prophet Muhammad (ﷺ)?

Never did I, see the Messenger of Allah (ﷺ) after the revelation (of these verses):” When Allah’s help and victory came.” observin- his prayer without making (this supplication) or he said in it (supplication): Hallowed be Thee, my Lord, and with Thy praise, O Allah, forgive me.