What did Prophet Muhammad (saw) say when `Umar bin Al-Khattab asked whether he could buy a horse that he had given in charity?
 Narrated `Umar bin Al-Khattab:                     Once I gave a horse (for riding) in Allah's Cause. Later I saw it being sold. I asked Allah's Apostle (whether I could buy it). He said, "Don't buy it, for you should not get back what you have given in charity."