Musnad Ahmad 1156:45

Qaran ibn Tamam Abu Tamam al-Asadi narrated to us, he said: Muhammad ibn Abi Humayd narrated to us, from al-Muttalib ibn Abdullah al-Makhzumi, who said: I entered upon Umm Salamah, the wife of the Prophet, may Allah bless him and grant him peace, and she said: "O my son, shall I not tell you what I heard from the Messenger of Allah, may Allah bless him and grant him peace?" I said: "Yes, O my mother." She said: "I heard the Messenger of Allah, may Allah bless him and grant him peace, saying: 'Whoever spends on two daughters, or two sisters, or two female relatives, seeking the reward for spending on them, until Allah enriches them from His bounty, Mighty and Majestic is He, or suffices them, they will be a shield for him from the Fire.'"