Allah's Apostle ﷺ kept standing in prayer (for such long hours) that his feet were swollen. They (his Companions) said: Verily, Allah has pardoned for thee the earlier and the later of thine sins. Thereupon he said: Should I not prove myself to be a grateful servant (of Allah)?

قَامَ النَّبِيُّ ﷺ حَتَّى وَرِمَتْ قَدَمَاهُ قَالُوا قَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ قَالَ أَفَلاَ أَكُونُ عَبْدًا شَكُورًا