Mukhtasar Bukhari

Sayyiduna Mughirah bin Shu’bah (may Allah be pleased with him) narrates that the Prophet Muhammad (peace and blessings be upon him) used to stand (in prayer) so long that both his feet or (he said) both his shins would swell. So it was said to him (that do not exert yourself so much in worship), and he (peace and blessings be upon him) would reply: “Should I not be a grateful servant of Allah?”