Musnad Ahmad 652:31

Hashim narrated to us, Abu Bishr informed us, from Habib ibn Salim, from al-Nu’man ibn Bashir, who said: "I am the most knowledgeable of people, or among the most knowledgeable of people, regarding the time of the Messenger of Allah’s (may Allah bless him and grant him peace) Isha prayer. He used to pray it after the setting of the moon on the third night of the beginning of the month."