The Messenger of Allah (ﷺ) said: "Whoever forgets a prayer, let him pray it when he remembers it."
Sunan an-Nasa'i Book 6, Hadith 120
← Previous Hadith "I was praying Witr, and 'Abdullah was asked: 'Is there any Witr after the Adhan?' He said: "Yes, and after the Iqamah, and he narrated that the Prophet (ﷺ) slept and missed the prayer until the sun rose then prayed.'" And the wording is that of Yahya.

Sunan an-Nasa'i Book 6, Hadith 119 Next Hadith → "The Messenger of Allah (ﷺ) was asked about a man who slept and missed the prayer, or forgot it. He said: 'The expiation for that is to pray it when he remembers it.'"

Sunan an-Nasa'i Book 6, Hadith 121