Midrash sur Les Nombres 28:10

(Bamidbar 28:10) "the burnt-offering of the Sabbath on its Sabbath": And not the burnt-offering of Sabbath eve (i.e., its limbs and fat-pieces), on the Sabbath, (but on Sabbath eve.) "the burnt-offering of the Sabbath on its Sabbath": And not the burnt-offering of this Sabbath on another Sabbath. If one did not sacrifice (the mussaf offering) of this Sabbath, I might think that he could do so on the next Sabbath. It is, therefore, written "the burnt-offering of the Sabbath on its Sabbath" — "Once the day has passed, its sacrifice has passed." "in addition to the daily burnt-offering and its libation": We are hereby apprised that the mussafim (of Sabbath) are sacrificed between (the two daily offerings).