Musnad Ahmad 941:22

Abu Salamah al-Khuza'i narrated to us, Malik informed us, from Muhammad ibn al-Munkadir and Abu al-Nadr, the freed slave of 'Umar ibn 'Ubayd Allah ibn Ma'mar, from 'Amir ibn Sa'd ibn Abi Waqqas, from his father, that he asked Usamah ibn Zayd: "What did you hear from the Messenger of Allah, may Allah bless him and grant him peace, regarding the plague?" Usamah said: "I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'It is a punishment that was sent upon a group of the Children of Israel, or upon a group of those who were before you'—the doubt is in the hadith—'so if you hear of it in a land, do not advance toward it, and if it occurs in a land while you are in it, do not exit it fleeing from it.'" Abu al-Nadr said in his narration: "Do not let anything cause you to exit except fleeing from it."