Ali bin Ms'hr علي بن مسهر · The Book on Fasting

"A man asked Ali: "Which month do you order me to fast after the month of Ramadan?' He said to him, 'I have not heard anyone ask this except for a man whom I heard asking the Messenger of Allah while I was sitting with him. He said: "O Messenger of Allah! Which month do you order me to fast after the month of Ramadan?" He said: "If you will fast after the month of Ramadan, then fast Al-Muharram, for…

"We would menstruate during the time of the Messenger of Allah, then when we became pure we were ordered to make up the fasts but we were not ordered to make up the Salat."