Deuteronomy 3:28

וצו את יהושע AND GIVE JOSHUA CHARGE regarding the cumbrance, the burdens and strifes that he will have to bear (cf. Deuteronomy 1:12). וחזקהו ואמצהו AND STRENGTHEN HIM AND MAKE HIM FIRM through thy words, so that he may not become faint-hearted, saying, “Just as my master was punished on account of them, so eventually will I be punished on account of them and not enter the land. I promise him “that he shall pass over [before this people] and he shall cause [them] to inherit [the land]”” (cf. Sifrei Devarim 29:9). כי הוא יעבר (this may mean: if he passes) — If he will pass before them, they will possess the land, and if not, they will not possess it. So, indeed, you find that when he sent some of the people against Ai and he remained in the camp, “the men of Ai smote of them [thirtysix men]” (Joshua 7:5). And when he fell on his face, He said to him, קם לך: the verb is written קם (without ו, so that it may be read קָם) i.e. “It is thou who standest in thy place and sendest My children to war, who hast brought about this defeat. Why is it that thou fallest on thy face? Did I not thus tell thy master, Moses: If he will pass, they will pass on, but if not, they will not pass on? (Sifrei Devarim 29:9).

וְצַ֥ו אֶת־יְהוֹשֻׁ֖עַ וְחַזְּקֵ֣הוּ וְאַמְּצֵ֑הוּ כִּי־ה֣וּא יַעֲבֹ֗ר לִפְנֵי֙ הָעָ֣ם הַזֶּ֔ה וְהוּא֙ יַנְחִ֣יל אוֹתָ֔ם אֶת־הָאָ֖רֶץ אֲשֶׁ֥ר תִּרְאֶֽה׃

But charge Yehoshua, and encourage him, and strengthen him: for he shall go over before this people, and he shall cause them to inherit the land which thou shalt see.