Musnad Ahmad 25:438

'Affan narrated to us, Wuhayb narrated to us, 'Abdullah ibn Tawus narrated to us, from 'Ikrimah ibn Khalid, from Ibn 'Abbas: "The Prophet, may Allah bless him and grant him peace, stood up at night to pray. I stood up and performed ablution, then I stood to his left. He pulled me and drew me, and placed me to his right. He prayed thirteen rak'ahs, his standing in them being equal."