פירוש על קידושין 39:8

R. Nahman b. Yitzchak interprets R. Eliezer’s opinion to mean as follows: If he came in without a wife, the master cannot force him to take a wife (“if he came in single, he goes out single”). But if he came in with a wife, the master can force him to take another wife.
I should note that the “pshat” of the verse is almost certainly that if the slave came in unmarried, he goes out unmarried, and if he came in married, his wife and children go out with him. But this is a hard verse for the rabbis to countenance for it is too obvious. If he came in single, why would he go out anything but single? He has no wife! And if he came in married with his kids, of course his kids and wife go out with him! They were not bought as slaves. Therefore, the rabbis have to find alternative meanings for this verse.