مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4059
Musnad of Abdullah bin Mas'ood
It was narrated from 'Abdullah from The Prophet (ﷺ): “What a bad thing for one of you to say: I forgot such and such a verse. Rather he was caused to forget.”
Musnad Ahmad 4085Its isnad is saheeh, al-Bukhari (5039)]