Musannaf Ibn Abi Shayba 19:265

Abu Bakr narrated to us, he said: Ghassan ibn Mudar narrated to us, from Sa'id ibn Yazid, from Abu Nadra, who said: Ibn Abbas was asked, "What is the prescribed punishment for the sodomite?" He said: "One should look for the highest building in the village, and he should be thrown from it headfirst. Then, he should be followed with stones."