2,773. Offering Reuvein's Korbanos
Continuing the case of Reuvein, who is prohibited to benefit from Shimon.
Hilchos Nedarim 6:5
If Shimon is a kohein, he may offer sacrifices brought by Reuvein. The is because kohanim operate on behalf of Hashem; they are not the agents of those who bring offerings. Shimon may marry his adult daughter to Reuvein with her consent, but if she is a maiden (naarah), she is under his jurisdiction and it is prohibited. This is because it’s comparable to giving him a servant girl.
Hilchos Nedarim 6:6
Shimon may separate trumah for Reuvein, and he may separate tithes with his consent. “With his consent” means that Reuvein says that whoever wants to separate trumah may do so. He may not tell Shimon specifically to do so for him because this would make Shimon his agent, which is considered benefitting from him.