Sifrei Bamidbar 30

(Bamidbar 6:11) "And the Cohein shall make one a sin-offering and one a burnt-offering": The Cohein shall designate them; one for a sin-offering and one for a burnt-offering. This tells me of designation by the Cohein. Whence do I derive designation by the owner? Do you ask? It follows a fortiori, viz.: If one (the Cohein), who is not permitted to dedicate it (as an offering), is permitted to designate it, then one (the owner), who is permitted to dedicate it, how much more so is he permitted to designate it! And thus, (that designation is by the owner) is it written in respect to a woman who has given birth (Vayikra 12:8) "Then she shall take two turtle-doves or two young pigeons, one for a burnt-offering and one for a sin-offering" — whence we find that there is designation by the Cohein and designation by the owner — whence we find that there is an unqualified ken (the couple of sacrificial birds, [in the instance of the Nazirite, where the Cohein designates them]) and a qualified ken, (in the instance of the child-bearing woman, where she herself designates them, one as a sin-offering and one as a burnt-offering.) "and he shall atone for him for having sinned against the soul": Now against which soul did he sin that he needs atonement? (His sin is) that he deprived himself of wine. Now does this not follow a fortiori, viz.: If one who deprives himself of wine needs atonement, how much more so, one who deprives himself of everything (by fasting)! R. Yishmael says: Scripture speaks of a Nazirite who made himself tamei (by a dead body), it being written "and he shall atone for him by having sinned (i.e., for having defiled himself) by the soul" — a dead soul. "and he shall make holy his head on that day": On the day of his shaving. These are the words of Rebbi. R. Yossi b. Yehudah says: On the day of the bringing of his offerings.