As-Salaam Alaikum Wa-Rahmatullahi Wa-Barakatuhu

Zakat – 20th Sha'aban 1433 (10th July 2012)

Narrated 'Umar (Radi-Allahu 'anhu):

Once I gave a horse in Allah's Cause (in charity) but that person did not
take care of it. I intended to buy it, as I thought he would sell it at a
low price. So, I asked the Prophet (Sallallahu 'Alaihi Wa Sallam) about it.
He said, "Neither buy, nor take back your alms which you have given, even
if the seller were willing to sell it for one Dirham, for he who takes back
his alms is like the one who swallows his own vomit."

Bukhari Vol. 2 : No. 567