Musnad Ahmad 652:69

'Affan and Surayj narrated to us, they said: Abu 'Awanah narrated to us, from Abu Bishr, from Bashir ibn Thabit, from Habib ibn Salim, from an-Nu'man ibn Bashir, who said: "By Allah, I am among the people who know best the time of this prayer, the last 'Isha' prayer. The Messenger of Allah, peace and blessings of Allah be upon him, used to pray it at the setting of the moon on the third night."