It is narrated from Amir bin Sa'd that Sayyiduna Sa'd (may Allah be pleased with him) was riding to his palace in the valley of al-Aqiq when he found a slave cutting trees, so he seized his belongings. When he returned, the slave's owners came to him and asked for their things back. He said: "Allah forbid that I should return something that the Messenger of Allah (peace and blessings be upon him) has granted me as a reward!" So he did not return anything. This hadith is sahih (authentic) on the condition of the two Shaykhs (Bukhari and Muslim), but they did not record it.