Sahih Muslim Book 4, Hadith Number 1390.

Chapter : Permission to remain away from the congregational prayer for any valid reason.

Abdullah b. al-Mukhtar heard Musa b. Anas narrating on the authority of Anas b. Malik that the Messenger of Allah (may peace be upon him) led him, his mother or his aunt in prayer. He made me, stand on his right side and made the woman stand, behind us.