Narrated 'Umar bin Al-Khattab (Radi-Allahu 'anhu):
I gave a horse in Allah's Cause. The person to whom it was
given, did not look after it. I intended to buy it from him,
thinking that he would sell it cheap. When I asked the
Prophet (S.A.W) he said,"Don't buy it, even if he gives it to
you for one Dirham, as the person who takes back what he
has given in charity, is like a dog that swallows back its
vomit."
[Bukhari Vol. 3 : No. 792]