Musnad Ahmad 1153:730

Abu Sa’id narrated to us, he said: Za’idah narrated to us, he said: Al-Suddi narrated to us, from ‘Abdullah al-Bahiy, he said: ‘A’ishah narrated to me, that the Messenger of Allah (peace and blessings of Allah be upon him) was in the mosque, and he said to the girl: "Hand me the prayer mat (khumrah)." She said: He wanted to spread it out so he could pray upon it. She said: "I am menstruating." He said: "Indeed, your menstruation is not in your hand."