مُسْنَدُ أَحْمَدَ
Musnad Ahmad 4046
Musnad of Abdullah bin Mas'ood
It was narrated from ‘Abdullah (رضي الله عنه) that The Prophet (ﷺ) prayed Zuhr or ‘Asr with five rak’ahs, then he did the two prostrations of forgetfulness. Then the Messenger of Allah (ﷺ) said: "These two prostrations are for anyone among you who thinks that he did more or less."
Musnad Ahmad 4072Hasan, this isnad is da’eef. It is a repeat of 3883]