Genesis 29:34

And she conceived again, and bare a son
A third time, as soon as she well could after the former birth: and said, now this time will my husband be joined to me;
in greater affection and stronger ties of love, and cleave unto her: because I have born him three sons;
which she considered as a threefold cord, binding his affections to her, which could not be easily broke; and therefore was his name called Levi;
which signifies "joined"; from him the Levites sprung, and had their name.