TT #221 · Parashas Shoftim · Sixth Aliyah · Passuk 19:14
You shall not move your fellow’s boundary marker, which the first ones set, in your inheritance that you will inherit in the land that the Eternal your God is giving you to possess.
Torah Temimah points to Sifrei Devarim 188.
TT lemma: אֲשֶׁר גָּבְלוּ רִאשׁוֹנִים.
English: ‘Which the first ones set’ – in the days of Yehoshua.
Derash on the original allotment (Sifrei) — the ‘first ones’ are those who divided the Land at the conquest.
The boundaries fixed at the time of the original inheritance under Yehoshua may not be altered by later generations.