"The Prophet (ﷺ) passed by old man walking (while supported) between his two sons, so he said: 'What is the matter with this one?' They said: "O Messenger of Allah! He vowed to walk.' He said: 'Verily Allah [the Mighty and Sublime] is in no need of this person punishing himself.'" He said: "So he ordered him to ride."
حَدَّثَنَا أَبُو مُوسَى، مُحَمَّدُ بْنُ الْمُثَنَّى حَدَّثَنَا خَالِدُ بْنُ الْحَارِثِ، حَدَّثَنَا حُمَيْدٌ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، قَالَ مَرَّ النَّبِيُّ صلى الله عليه وسلم بِشَيْخٍ كَبِيرٍ يَتَهَادَى بَيْنَ ابْنَيْهِ فَقَالَ " مَا بَالُ هَذَا " . قَالُوا يَا رَسُولَ اللَّهِ نَذَرَ أَنْ يَمْشِيَ . قَالَ " إِنَّ اللَّهَ عَزَّ وَجَلَّ لَغَنِيٌّ عَنْ تَعْذِيبِ هَذَا نَفْسَهُ " . قَالَ فَأَمَرَهُ أَنْ يَرْكَبَ .
Tirmizi
The Book on Vows and Oaths • Hadith 1571