Midrash for Bava Metzia 65:26

(Devarim 22:1) "You shall not see (the ox of your brothers or his lamb straying and [you shall] ignore them. Return shall you return them to your brother." "You shall not see": I might think, even if he were a mil away; it is, therefore, written (Shemoth 23:4) "If you encounter (the ox of your foe, etc.") If "If you encounter," I might think, literally; it is, therefore, written "You shall not see." How is this to be resolved? The sages estimated one-seventh of a mil, a ris.