This hadith has been transmitted on the authority of Mughira b. Shu'ba and the words are: 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)?

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَابْنُ، نُمَيْرٍ قَالاَ حَدَّثَنَا سُفْيَانُ، عَنْ زِيَادِ بْنِ عِلاَقَةَ، سَمِعَ الْمُغِيرَةَ بْنَ شُعْبَةَ، يَقُولُ قَامَ النَّبِيُّ ﷺ حَتَّى وَرِمَتْ قَدَمَاهُ قَالُوا قَدْ غَفَرَ اللَّهُ لَكَ مَا تَقَدَّمَ مِنْ ذَنْبِكَ وَمَا تَأَخَّرَ . قَالَ " أَفَلاَ أَكُونُ عَبْدًا شَكُورًا " .