al-Mughira bin 'Abdullah المغيرة بن عبد الله بن أبي عقيل · Prayer at Night (Tahajjud)

The Prophet (ﷺ) used to stand (in the prayer) or pray till both his feet or legs swelled. He was asked why (he offered such an unbearable prayer) and he said, "should I not be a thankful slave."