Parashas Toldos · Passuk 26:2
Hashem appeared to him and said, “Do not go down to Egypt; dwell in the land that I will tell you.
Rashi on Bereishis 26:2 (classical source on this passuk; not listed as a numbered Torah Temimah unit here).
Lemma / focus: אל תרד מצרימה.
English: For he intended to go down to Egypt as his father had gone down in the days of famine. He said to him: Do not go down to Egypt, for you are a perfect burnt-offering, and outside the Land is not fitting for you.
Derash on the verse (Rashi / midrash) — not a formal named middah of the 13: the prohibition is linked to the Akeidah status of Yitzchak as an offering.
Hashem forbade Yitzchak to go down to Egypt: he is a perfect offering from the Akeidah, and life outside the Land is not fitting for him.