Sunan an-Nasā'ī 1344

The full narration

It was narrated from Aishah that:When the Messenger of Allah (ﷺ) sat in a gathering or prayed, he said some words, and 'Aishah asked him about those words. He said: "If he has spoken some good words (and he says this statement of remembrance), it will be a seal for them to preserve them until the Day of Resurrection, and if he has said something other than that, it (these words) will be an expiation for him: 'Subhanak Allahumma wa bihamdika, astaghfiruka wa atubu ilayk (Glory and praise be to You, O Allah, I seek Your forgiveness and I repent to You)