Sunan Abi Dawud, Hadith 442 ⓘ
Anas b. Malik reported the Prophet as saying: If any one forgets a prayer or oversleeps, he should observe it when he remembers it ; there is no expiation for it except that.
حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا هَمَّامٌ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ " مَنْ نَسِيَ صَلاَةً فَلْيُصَلِّهَا إِذَا ذَكَرَهَا لاَ كَفَّارَةَ لَهَا إِلاَّ ذَلِكَ " .
also referenced under: Hadith 442 (DarusSalam) & Book 2, Hadith 442 (USC-MSA)