question #2 Sahih al-Bukhari 796, Book 10, Hadith 191 : How can one’s response during prayer lead to the forgiveness of past sins?

Allah’s Messenger (ﷺ) said, “When the Imam says, “Sami`a l-lahu liman hamidah,” you should say,
“Allahumma Rabbana laka l-hamd.” And if the saying of any one of you coincides with that of the
angels, all his past sins will be forgiven.”