Musnad Ahmad 1163:15

Sufyan narrated to us, from Manbudh, from his mother, who said: I was with Maymunah when Ibn Abbas came to her. She said: "O my son, why is your hair disheveled?" He said: "The mother of Ammar, my hairdresser, is menstruating." She said: "O my son, and where is the menstruation in the hand?" "The Messenger of Allah (peace and blessings of Allah be upon him) used to enter upon one of us while she was menstruating, and he would place his head in her lap and recite the Quran while she was menstruating. Then one of us would stand up with her prayer mat and place it in the mosque while she was menstruating." "O my son, and where is the menstruation in the hand?"