Sifrei Bamidbar 38

(Bamidbar 6:21) "This is the law of the Nazirite": This (i.e., what we have learned of the offerings) tells me only of the time (of the Temple, when there are offerings). Whence do we derive (that Naziritism obtains) in all generations? From "This is the (perpetual) law." These are the words of R. Yoshiyah. R. Yonathan says: This (i.e., "This is the law") is stated by way of summation. "his offering to the L-rd for his Naziritism": i.e., his offering to the L-rd is contingent upon his Naziritism, and his Naziritism is not contingent upon his offering (i.e., if he vows to bring the offering, he does not thereby become a Nazirite.) "his offering to the L-rd for his Naziritism": and not the offering of others for his Naziritism (i.e., if he said "I will be a Nazirite on condition that others bring the Nazirite offering," he has said nothing.) "aside from what his hand attains": We are hereby apprised that if he said: I am a Nazirite on condition that I shave over a hundred burnt-offerings and a hundred peace-offerings, I recite over him "According to his vow that he vows thus shall he do." I might think (that the same applies) even if he said: I am a Nazirite on condition that I shave over a hundred sin-offerings and a hundred guilt-offerings. It is, therefore, written "that he vows." It applies only to offerings that are brought as vows and gifts (to exclude the above). I might think that even if he said "I undertake five Naziritisms (on condition) that I shave one shaving for all," I recite over him "according to his vow that he vows"; it is, therefore, written "thus shall he do according to the law of his Naziritism" (i.e., he must shave for each Naziritism individually). R. Eliezer b. Shamua and R. Yochanan Hasandlar asked R. Shimon b. Yochai: If one were a clean Nazirite (as opposed to one defiled by the dead) and a leper, may he perform one shaving, which satisfies both his Naziritism and his leprosy? He answered: Is this possible? If each shaved in order to grow hair, or if each shaved in order to remove hair, your question would be in place; but the leper shaves in order to grow hair (for he must shave a second time after his count (viz. Vayikra 14:9), and the Nazirite shaves in order to remove hair, so how can one shaving serve for both? — If not, let it (one shaving) suffice for the days of his (the leper's state of) confirmation and his (the Nazirite's) counting, (where both shave in order to remove hair). He answered: If both were before the sprinkling of the blood, your question would be in place. But the (confirmation) shaving of the leper is before the sprinkling of the blood, and that of the Nazirite, after the sprinkling of the blood. They responded: If it (one shaving) does not suffice for the days of his leprosy and a clean Nazirite, let it suffice for the days of his leprosy and an unclean (i.e., defiled) Nazirite. He answered: An unclean Nazirite in the days of his (the leper's) counting — the intent of one (the leper) is to grow hair, and of the other (the Nazirite), to remove it. An unclean Nazirite in the days of his (the leper's) confirmation, (even though the intent of both is to remove it) — one, (the leper, shaves) before the administration of the waters of the red heifer; the other, (the Nazirite, shaves) after the administration of the waters. The conditions (for a single shaving) cannot be satisfied, neither in the days of his (the leper's) consummation nor in the days of his counting; neither with an unclean (Nazirite) nor with a clean one.