Sahih al-Bukhari 173
Sahih al-Bukhari · Book 4: Ablutions (Wudu') · If a dog drinks from the utensil of any one of you then it is essential to wash it seven times
Narrated Abu Huraira:
حَدَّثَنَا إِسْحَاقُ ، أَخْبَرَنَا عَبْدُ الصَّمَدِ ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ بْنِ دِينَارٍ ، سَمِعْتُ أَبِي ، عَنْ أَبِي صَالِحٍ ، عَنْ أَبِي هُرَيْرَةَ ، عَنِ النَّبِيِّ صلى الله عليه وسلم " أَنَّ رَجُلاً رَأَى كَلْبًا يَأْكُلُ الثَّرَى مِنَ الْعَطَشِ، فَأَخَذَ الرَّجُلُ خُفَّهُ فَجَعَلَ يَغْرِفُ لَهُ بِهِ حَتَّى أَرْوَاهُ، فَشَكَرَ اللَّهُ لَهُ فَأَدْخَلَهُ الْجَنَّةَ " .
The Prophet (ﷺ) said, "A man saw a dog eating mud from (the severity of) thirst. So, that man took a shoe (and filled it) with water and kept on pouring the water for the dog till it quenched its thirst. So Allah approved of his deed and made him to enter Paradise."