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." (Using translation from Bukhārī 173)
عَنِ النَّبِيِّ ﷺ أَنَّ رَجُلًا رَأَى كَلْبًا يَأْكُلُ الثَّرَى مِنَ الْعَطَشِ فَأَخَذَ الرَّجُلُ خُفَّهُ فَجَعَلَ يَغْرِفُ لَهُ بِهِ الْمَاءَ حَتَّى أَرْوَاهُ فَشَكَرَ اللهُ ﷻ لَهُ فَأَدْخَلَهُ الْجَنَّةَ