From Sahih Muslim (Hadith 250):
Abu Dharr reported:I said: Messenger of Allah, which of the deeds is the best? He (the Holy Prophet) replied: Belief in Allah and Jihad in His cause. I again asked: Who is the slave whose emancipation is the best? He (the Holy Prophet) replied: One who is valuable for his master and whose price is high. I said: If I can't afford to do it? He (the Holy Prophet) replied: Help an artisan or make anything for the unskilled (labourer). I (Abu Dharr) said: Messenger of Allah, you see that I am helpless in doing some of these deeds. He (the Holy Prophet) replied: Desist from doing mischief to the people. That is the charity of your person on your behalf
Reference: Muslim 250