וַיֹּ֧אמֶר יְהוֹשֻׁ֛עַ אֶל־הָעָ֖ם הִתְקַדָּ֑שׁוּ כִּ֣י מָחָ֗ר יַעֲשֶׂ֧ה יְהוָ֛ה בְּקִרְבְּכֶ֖ם נִפְלָאֽוֹת׃
Josua sprach zum Volke: Seid bereit, denn morgen wird der Herr in eurer Mitte Wunder thun.
Rashi on Joshua
And Yehoshua said. This was on the third day, and the thirtieth day of mourning [for Moshe] was on the first of the three days.
Rashi on Joshua
הִתְקַדָשׁוּ usually means sanctify yourselves, but here it means prepare yourselves.