Rashi on Numbers 3:9/רש"י על במדבר ג׳:ט׳

1נתונים המה לו THEY ARE GIVEN UNTO HIM as a help.

2מאת בני ישראל has the same meaning as FROM AMONG THE MIDST OF (מתוך) THE CHILDREN OF ISRAEL, that is to say, they have been set aside from among the rest of the congregation for this purpose by a decree of the Omnipresent, and it is He who gave them (the Levites) to him, as it is said (Numbers 8:19) “And “I” have given the Levites as a gift [to Aaron]”.