Musannaf Ibn Abi Shaybah

Hazrat Saeed bin Jubair narrates that the ruler of Abyssinia, Abu Yaksum, came and with him were elephants (as well). When he reached the Haram, his elephant sat down and refused to enter the Haram. The narrator says that when Abu Yaksum directed the elephant to return, the elephant would run back swiftly, but when he intended to go towards the Haram, the elephant refused. Then, small white birds were sent upon them, each of which had stones the size of chickpeas in their beaks. Whomever those stones fell upon, he would be destroyed.