Musnad Ahmad 1163:53

Muhammad ibn Ja‘far and Yahya ibn Sa‘id narrated to us, from Shu‘bah, who said: Al-Hakam narrated to me, saying: I asked Miqsam, saying: "Should I perform Witr with three [rak‘ahs], then go out to the prayer for fear that I might miss it?" He said: "It is not appropriate except with five or seven." So I informed Mujahid and Yahya ibn al-Jazzar of his statement, and they both said to me: "Ask him: from whom?" So I asked him, and he said: "From the trustworthy one, from the trustworthy one, from Maymunah and ‘Aishah, from the Prophet, peace and blessings of Allah be upon him."