Musnad Ahmad 8:176

Suwayd ibn ‘Amr al-Kalbi narrated to us, Aban narrated to us, Yahya narrated to us, from al-Hadrami ibn Lahiq, from Sa‘id ibn al-Musayyib, from Sa‘d ibn Malik: That the Messenger of Allah (may Allah bless him and grant him peace) said: "If the plague is in a land, do not enter it, and if it is in a land and you are in it, do not flee from it."