Al-Adab Al-Mufrad, Book 20, Hadith 373 (English) ⓘ

Mu'awiya ibn Qurra reported that his father said, "A man said, 'Messenger of Allah, I was going to slaughter a sheep and then I felt sorry for it (or 'sorry for the sheep I was going to slaughter').' He said twice, 'Since you showed mercy to the sheep, Allah will show mercy to you.'"

حَدَّثَنَا مُسَدَّدٌ، قَالَ‏:‏ حَدَّثَنَا إِسْمَاعِيلُ بْنُ إِبْرَاهِيمَ، قَالَ‏:‏ حَدَّثَنَا زِيَادُ بْنُ مِخْرَاقٍ، عَنْ مُعَاوِيَةَ بْنِ قُرَّةَ، عَنْ أَبِيهِ قَالَ‏:‏ قَالَ رَجُلٌ‏:‏ يَا رَسُولَ اللهِ، إِنِّي لَأَذْبَحُ الشَّاةَ فَأَرْحَمُهَا، أَوْ قَالَ‏:‏ إِنِّي لَأَرْحَمُ الشَّاةَ أَنْ أَذْبَحَهَا، قَالَ‏:‏ وَالشَّاةُ إِنْ رَحِمْتَهَا، رَحِمَكَ اللَّهُ مَرَّتَيْنِ‏.‏