Numbers 8:25

ולא יעבד עוד [AND FROM THE AGE OF FIFTY YEARS HE SHALL CEASE WAITING UPON THE SERVICE] AND SHALL DO NO MORE SERVICE — the service of bearing loads on the shoulder, but he still returns (i. e. may be called upon) for closing the Temple gates, for the service of singing and for loading sacred articles upon the wagons; for this is the meaning of (v. 26) “But he shall serve את אחיו” i. e. together with his brethren, just as the Targum renders it (not, “he shall serve his brethren, i. e. wait upon them) (cf. Sifrei Bamidbar 63).

וּמִבֶּן֙ חֲמִשִּׁ֣ים שָׁנָ֔ה יָשׁ֖וּב מִצְּבָ֣א הָעֲבֹדָ֑ה וְלֹ֥א יַעֲבֹ֖ד עֽוֹד׃

and from the age of fifty years they shall go out of the ranks of the service, and shall serve no more: