From Sahih Muslim (Hadith 1801):
Ibn `Abbas reported:(My father) Al-`Abbas sent me to the Messenger of Allah (ﷺ) and he was in the house of my mother's sister Maimuna and I 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
Reference: Muslim 1801