Sunan Ibn Majah, Book 2, Hadith 29 (In-Book) ⓘ
It was narrated that Anas bin Malik said: 'The Prophet was asked about a man who forgets prayer or sleeps and misses it. He said: 'he performs it when he remembers it.'"
حَدَّثَنَا نَصْرُ بْنُ عَلِيٍّ الْجَهْضَمِيُّ، حَدَّثَنَا يَزِيدُ بْنُ زُرَيْعٍ، حَدَّثَنَا حَجَّاجٌ، حَدَّثَنَا قَتَادَةُ، عَنْ أَنَسِ بْنِ مَالِكٍ، قَالَ سُئِلَ النَّبِيُّ ـ صلى الله عليه وسلم ـ عَنِ الرَّجُلِ يَغْفُلُ عَنِ الصَّلاَةِ أَوْ يَرْقُدُ عَنْهَا قَالَ " يُصَلِّيهَا إِذَا ذَكَرَهَا " .
also referenced under: Hadith 695 (Reference) & Volume 1, Book 2, Hadith 695 (DarusSalam)