Musnad Ahmad 31:695

Bahz narrated to us, Shu'bah narrated to us, from 'Abd al-Rahman ibn al-Asbahani, who said: I heard Dhakwan narrating from Abu Sa'id al-Khudri, who said: The women said: "O Messenger of Allah, the men have overcome us [in gaining access to you], so appoint a day for us." So he promised them a day. The Messenger of Allah (peace and blessings of Allah be upon him) said: "Any woman among you who sends ahead three of her children, they will be a shield for her against the Fire." A woman said: "O Messenger of Allah, I have sent ahead two." He said: "And two."