Genesis 15:16

ודור רביעי BUT A FOURTH GENERATION — i.e. after they go into exile in Egypt they will be there three generations, and the fourth will return to this land (הֵנָה hither). For He was then speaking to him in the land of Canaan and it was there that He made this covenant, as it is written (v.7) “to give thee this land to inherit it”. Thus it really was: Jacob went down to Egypt. Go and count up his generations: Judah, Perez, Hezron— and Caleb (whose father Jephuneh is identified with Hezron, see Sotah 11b) was amongst those who entered the land of Canaan. כי לא שלם עון האמורי FOR THE INIQUITY OF THE AMORITE IS NOT YET FULL enough that he should be driven out of his land until that time, for the Holy One, blessed be He, does not exact punishment from any nation until its measure is full, as it is said, (Isaiah 27:8) “In her full measure wilt thou contend with her when thou sendest her away” (Sotah 9a).

וְד֥וֹר רְבִיעִ֖י יָשׁ֣וּבוּ הֵ֑נָּה כִּ֧י לֹא־שָׁלֵ֛ם עֲוֺ֥ן הָאֱמֹרִ֖י עַד־הֵֽנָּה׃

But in the fourth generation they shall come back here, for the iniquity of the Emori is not yet full.