פירוש על עבודה זרה 74:9

The rabbis use a discrepancy in the verses to prove that there is a difference between a case where the person is still in contact with the dead body (he transmits seven-day impurity) and a case where he is no longer in contact with the dead body (he transmit one-day impurity). The verse that says he shall be impure, which means seven days, refers to a person who touches another person who is still in contact with the dead body. And the verse that says that he is only impure until evening refers to one who is no longer in contact with a dead body.