Amr bin al-Sharid (may Allah have mercy on him) narrates from his father, Sayyiduna al-Sharid (may Allah be pleased with him), who said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever kills a sparrow without reason, it will cry out to Allah on the Day of Resurrection and say: O my Lord! This servant of Yours killed me without reason, and he did not kill me for any benefit."
Hadith Referenceالمعجم الكبير للطبراني / باب الشين / 7214