Musnad Ahmad 128:1

Isma'il ibn Ibrahim narrated to us, Ziyad ibn Mikhraq narrated to us, from Mu'awiyah ibn Qurrah, from his father, that a man said: "O Messenger of Allah, I indeed slaughter a sheep, and I have mercy upon it"—or he said: "I indeed have mercy upon the sheep that I should slaughter it." He said: "And the sheep, if you have mercy upon it, Allah will have mercy upon you." And the sheep, if you have mercy upon it, Allah will have mercy upon you.