Sahih Bukhari
Obligatory Charity Tax (Zakat)
Volume: 002 / Book Number: 024 / Hadith Number: 515
Narrated Asma' bint Abu Bakr:
that she had gone to the Prophet and he said, "Do not shut your money bag; otherwise Allah too will with-hold His blessings from you. Spend (in Allah's Cause) as much as you can afford. "