Abu Hurayrah (May Allah be pleased with him) reported: Allah’s Messenger (Peace and blessings be upon Him) encouraged the people, without making it an absolute command, to perform Qiyaam during Ramadan. He (Peace and blessings be upon Him) used to say: “Whoever stands (in Qiyaam) in Ramadan out of faith and expectation (of Allah’s reward), all his previous sins will be forgiven.” [Saheeh Muslim]