Sunan an-Nasa'i 3853
It was narrated that Anas said:
"The Messenger of Allah passed by an old man who was being supported between two men and said: 'What is the matter with him?' They said: 'He vowed to walk.' He said: 'Allah has no need for him to torture himself. Tell him to ride.'" So he was told to ride.
أَخْبَرَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، قَالَ حَدَّثَنَا خَالِدٌ، قَالَ حَدَّثَنَا حُمَيْدٌ، عَنْ ثَابِتٍ، عَنْ أَنَسٍ، قَالَ مَرَّ رَسُولُ اللَّهِ صلى الله عليه وسلم بِشَيْخٍ يُهَادَى بَيْنَ اثْنَيْنِ فَقَالَ ‏"‏ مَا بَالُ هَذَا ‏"‏ ‏.‏ قَالُوا نَذَرَ أَنْ يَمْشِيَ ‏.‏ قَالَ ‏"‏ إِنَّ اللَّهَ غَنِيٌّ عَنْ تَعْذِيبِ هَذَا نَفْسَهُ مُرْهُ فَلْيَرْكَبْ ‏"‏ ‏.‏ فَأَمَرَهُ أَنْ يَرْكَبَ ‏.‏