Musnad Ahmad 27:151

Sufyan narrated to us, from Ibn Abi Najih, from Isma'il ibn 'Abd al-Rahman ibn Dhu'ayb, from the tribe of Banu Asad ibn 'Abd al-'Uzza, who said: We went out with Ibn 'Umar to al-Hima. When the sun set, we were hesitant to say to him: "The prayer," until the whiteness of the horizon disappeared and the darkness of the night (the *'isha*) had passed. He dismounted and prayed with us three [rak'ahs] and two [rak'ahs]. Then he turned to us and said: "This is how I saw the Messenger of Allah, may Allah bless him and grant him peace, do."