It is narrated from Sayyiduna Hakim bin Hizam (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) gave him one dinar and sent him to buy a sacrificial animal for him. He bought the animal and then sold it for two dinars; then he bought (another) goat for one dinar and brought back the remaining dinar. "The Prophet (peace and blessings be upon him) supplicated for blessing for him and ordered him to give that dinar in charity."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3120