Sahih Muslim
The Book of Prayers (Kitab Al-Salat)
Book Number: 004 / Hadith Number: 1684
Ibn 'Abbas reported: (My father) Abbas sent me to the Apostle of Allah (may peace be upon him) and he was in the house of my mother's sister Maimuna and spent that night along with him. He (the Holy Prophet) got up and prayed at night, and I stood up on his left side. He caught hold of me from behind his back and made me stand on his right side.