Sifrei Bamidbar 71

(Bamidbar 9:14) "And if there live a proselyte among you, and he would offer a Pesach to the L-rd, etc.": I might think that as soon as he converts he offers a Pesach; it is, therefore, written (Ibid.) ("One statute shall there be for you, both) for the proselyte (and for the native"). Just as the native (offers) on the fourteenth (of Nissan), so, the proselyte. R. Shimon b. Elazar says: If one became a proselyte between the two Pesachs, I might think he observes Pesach Sheni; it is, therefore, written "for the proselyte and for the native." Just as the native who (is obligated to observe the first Pesach and) could not do so observes Pesach Sheni, so all, who are thus obligated, (to exclude from Pesach Sheni the proselyte in the above instance.) "according to the statue of the Pesach": This tells me only of the Pesach that the proselyte is equated with the native. Whence do I derive (the same for) all the mitzvoth of the Torah? From "One statute shall there be for you, both for the proselyte and for the native of the land." Scripture hereby equates the proselyte with the native in respect to all the mitzvoth of the Torah.