Musnad Ahmad 1170:1

Sufyan ibn 'Uyaynah narrated to me, he said: Ibn al-Munkadir heard Umaymah bint Ruqayqah saying: I pledged allegiance to the Messenger of Allah, may Allah bless him and grant him peace, among a group of women. He instructed us: "In what you are able and capable of." I said: Allah and His Messenger are more merciful to us than we are to ourselves. I said: O Messenger of Allah, let us pledge allegiance. He said: "I do not shake hands with women. My word to one woman is my word to one hundred women."