Sahih Bukhari Volume 2, Book 24, Hadith Number 545.
Narated By ‘Amr bin Al-Harith : Zainab, the wife of ‘Abdullah said, “I was in the Mosque and saw the Prophet (p.b.u.h) saying, ‘O women ! Give alms even from your ornaments.’ ” Zainab used to provide for ‘Abdullah and those orphans who were under her protection. So she said to ‘Abdullah, “Will you ask Allah’s Apostle whether it will be sufficient for me to spend part of the Zakat on you and the orphans who are under my protection?” He replied “Will you yourself ask Allah’s Apostle ?” (Zainab added): So I went to the Prophet and I saw there an Ansari woman who was standing at the door (of the Prophet) with a similar problem as mine. Bilal passed by us and we asked him, ‘Ask the Prophet whether it is permissible for me to spend (the Zakat) on my husband and the orphans under my protection.’ And we requested Bilal not to inform the Prophet about us. So Bilal went inside and asked the Prophet regarding our problem. The Prophet (p.b.u.h) asked, “Who are those two?” Bilal replied that she was Zainab. The Prophet said, “Which Zainab?” Bilal said, “The wife of ‘Adullah (bin Masud).” The Prophet said, “Yes, (it is sufficient for her) and she will receive a double rewards (for that): One for helping relatives, and the other for giving Zakat.”