Sifrei Bamidbar 35

(Bamidbar 6:18) "And the Nazirite shall shave at the door of the tent of meeting": Scripture here speaks of peace-offerings (i.e., that the Nazirite shaves after the sacrifice of the peace-offerings), it being written of them (Vayikra 3:2) "and he shall slaughter it at the door of the tent of meeting." You say this, but perhaps the verse is to be taken literally, (i.e., that he shaves at the door of the tent of meeting. If you say this, this is demeaning. Scripture states (Shemot 20:23): "Do not go up by steps, (but by a smooth ramp) upon My altar, so that your nakedness not be revealed upon it (by your having to take relatively long strides) — how much more so should he not shave (at the door of the tent of meeting)! What, then, is the intent of "And the Nazirite shall shave at the door of the tent of meeting"? Scripture refers here to the sacrifice of the peace-offerings (as above). R. Yitzchak says: Scripture speaks of the sacrifice of the peace-offerings. You say this? Perhaps it refers to (shaving at) the door of the tent of meeting, literally. It is, therefore, written (Bamidbar, Ibid.) "and he shall take the hair of the head of his Naziritism, etc." In the place (the room) where he cooks it (the peace-offerings), there shall he shave. Abba Channan says in the name of R. Eliezer: "And the Nazirite shall shave at the door of the tent of meeting." If the door was not open, he would not shave. "and he shall take the hair of the head of his Naziritism and he shall place it on the fire which is under the sacrifice of the peace-offerings." This tells me only of the peace-offerings. Whence do I derive (that he can do the same) under the sin-offering and under the guilt-offering? From "under the sacrifice" — in any event. This tells me only of (his shaving his hair in) the sanctuary. Whence do I derive the same for (his doing so) outside it? From "and he shall place it on the fire" — in any event.