מדרש על עמוס 7:15

Another interpretation (of Ps. 11:5): THE LORD TESTS THE RIGHTEOUS. R. Isaac said: In what does he test the righteous? In the pasture. David was tested in the pasture, as stated (in Ps. 78:71): HE BROUGHT HIM FROM FOLLOWING THE NURSING EWES TO SHEPHERD <HIS PEOPLE JACOB, EVEN ISRAEL HIS INHERITANCE>. Amos was tested in the pasture, [as stated (in Amos 7:15):] BUT THE LORD TOOK ME FROM FOLLOWING THE FLOCK. Moses also was tested in the pasture. Thus it is stated (in Exod. 3:1:) NOW MOSES WAS TENDING <THE FLOCK>….