Musannaf Ibn Abi Shayba 3:4863

Humaid ibn Abd al-Rahman narrated to us, from al-Hasan ibn Salih, from Mughirah, from Ibrahim, who said: The daughters of the Prophet, peace and blessings of Allah be upon him, and his wives used to menstruate, and the Prophet, peace and blessings of Allah be upon him, would command them to make up the fasts, but he would not command them to make up the prayers.