Sunan Abu Dawud
2447
Daif+2

Narrated AbdurRahman ibn Maslamah: AbdurRahman reported on the authority of his uncle that the people of the tribe Aslam came to the Prophet (ﷺ). He said (to them): Did you fast on this day? They replied: No. He said: Complete the rest of your day, and make atonement for it

DaifAl-Albani
DaifMuhammad Muhyi Al-Din Abdul Hamid