Musnad Ahmad 1156:205

Yazid narrated to us, he said: Sufyan al-Thawri narrated to us, from Ayyub ibn Musa, from Sa'id ibn Abi Sa'id al-Maqburi, from Abdullah ibn Rafi', from Umm Salamah, she said: I said: "O Messenger of Allah, I am a woman who braids my hair tightly; should I undo it for the ritual bath (ghusl) from sexual impurity (janabah)?" He said: "It is sufficient for you to pour three handfuls of water over your head."