Musnad Ahmad

It is narrated from Hazrat Abu Hurairah (may Allah be pleased with him) that a man came to the court of the Prophet and said, "O Messenger of Allah (peace and blessings be upon him), at what time is giving charity most rewarding?" The Noble Prophet (peace and blessings be upon him) said, "The best charity is that which you give while you are healthy, desiring wealth, fearing poverty, and hoping for a long life. Do not delay charity until the soul reaches the throat, and then you begin to say, 'Give this much to so-and-so and that much to so-and-so,' for by then it already belongs to so-and-so (the heirs)."