Sunan an-Nasai 18598
In-book no 3862أَخْبَرَنَا 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 .
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.