פירוש על קידושין 7:13

The same phenomenon occurs with Leviticus 22:10 which teaches that a “toshav and sakhir” who are part of a priest’s household may not eat terumah. What do these words mean, the rabbis ask? Toshav refers to a Hebrew slave acquired for perpetuity (meaning he was acquired for six years and then did not want to go free. He remains a slave until the Jubilee). And a sakhir is one acquired only for six years. Here too we can ask that if the one acquired for a longer time does not eat terumah, obviously one who is acquired for a lesser period does not eat. After all, he is less owned by the non-Jew. But if only one word had been stated, we would have said that it refers to one acquired for the shorter period—he does not eat terumah. But one acquired for perpetuity does eat terumah. Therefore, I need both words.

For it has not yet reached six years