Mishkat al-Masabih 29 Excellent Qualities and Description of the Prophet كتاب الفضائل والشمائل 68

وَعَنْ أَنَسٍ قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ إِذَا صَلَّى الْغَدَاةَ جَاءَ خَدَمُ الْمَدِينَةِ بِآنِيَتِهِمْ فِيهَا الْمَاءُ فَمَا يَأْتُونَ بإناءٍ إِلَّا غمسَ يدَه فِيهَا فرُبما جاؤوهُ بِالْغَدَاةِ الْبَارِدَةِ فَيَغْمِسُ يَدَهُ فِيهَا. رَوَاهُ مُسْلِمٌ

Anas told that when God’s messenger prayed the dawn prayer the servants in Medina brought their vessels containing water and they would not bring a vessel into which he did not dip his hand. They would often bring them on a cold morning and he would dip his hand into them. Muslim transmitted it.