Musnad Ahmad
It was narrated from Ibn ‘Abd Khair that his father said: I saw ‘Ali (رضي الله عنه) doing wudoo’. He washed the tops of his feet and said: Were it not that I saw the Messenger of Allah (ﷺ) washing the tops of his feet I would have thought that the bottoms of the feet were more deserving of being washed.
حَدَّثَنَا عَبْد اللَّهِ، حَدَّثَنَا إِسْحَاقُ بْنُ إِسْمَاعِيلَ، حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي السَّوْدَاءِ، عَنْ ابْنِ عَبْدِ خَيْرٍ، عَنْ أَبِيهِ، قَالَ رَأَيْتُ عَلِيًّا رَضِيَ اللَّهُ عَنْهُ تَوَضَّأَ فَغَسَلَ ظُهُورَ قَدَمَيْهِ وَقَالَ لَوْلَا أَنِّي رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَغْسِلُ ظُهُورَ قَدَمَيْهِ لَظَنَنْتُ أَنَّ بُطُونَهُمَا أَحَقُّ بِالْغَسْلِ.
Grade: Sahih (Darussalam)] (Darussalam)
Reference