Musnad Ahmad 941:56

Yahya ibn Abi Bukayr narrated to us, Shu'bah narrated to us, he said: Habib ibn Abi Thabit informed us, he said: I heard Ibrahim ibn Sa'd narrating that he heard Usamah ibn Zayd narrating to Sa'd that the Messenger of Allah (peace and blessings of Allah be upon him) said: "If you hear of the plague in a land, do not enter it, and if it occurs in a land while you are in it, do not leave it." He said: I said, "Did you hear him narrating this to Sa'd, and he did not deny it?" He said, "Yes."