Abu Sa'id reported God’s Messenger as saying, “If anyone over-sleeps and misses the witr, or forgets it, he should pray when he remembers and when he awakes.” Tirmidhi, Abu Dawud and Ibn Majah transmitted it.
Reported by At-Tirmidhi (No. 465). Cited in Mishkat al-Masabih (No. 1279).
"Whoever forgets a prayer should perform it as soon as he remembers it; there is no expiation for it except that: {and establish prayer to remember me.} [Surat Tā-ha: 14]"
Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported the Prophet (may Allah's peace and blessings be upon him) said: "If anyone sleeps before praying Witr or forgets it, let him pray it once he remembers it."