Qatada narrated on the authority of Anas b. Malik that the Messenger of Allah (ﷺ) said:He who forgets the prayer, or he slept (and it was omitted), its expiation is (only) that he should observe it when he remembers it.
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا عَبْدُ الأَعْلَى، حَدَّثَنَا سَعِيدٌ، عَنْ قَتَادَةَ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ قَالَ نَبِيُّ اللَّهِ صلى الله عليه وسلم " مَنْ نَسِيَ صَلاَةً أَوْ نَامَ عَنْهَا فَكَفَّارَتُهَا أَنْ يُصَلِّيَهَا إِذَا ذَكَرَهَا " .
Muslim
The Book of Mosques and Places of Prayer • Hadith 401