Numbers 9:1

בחדש הראשון [AND THE LORD SPAKE UNTO MOSES] IN THE FIRST MONTH — The section which appears at the commencement of this Book was not spoken before Eyar (the second month; cf. Numbers 1:1): you learn, therefore, that there is no “earlier” or “later” (no chronological order) in the Torah. But why, indeed, did not Scripture open the Book with this section? Because it implies something disparaging to Israel (Sifrei Bamidbar 64:1) — that during all the forty years they were in the wilderness they offered only this single Passover sacrifice (Tosafot on Kiddushin 38b s. v. הואיל)

וַיְדַבֵּ֣ר יְהֹוָ֣ה אֶל־מֹשֶׁ֣ה בְמִדְבַּר־סִ֠ינַ֠י בַּשָּׁנָ֨ה הַשֵּׁנִ֜ית לְצֵאתָ֨ם מֵאֶ֧רֶץ מִצְרַ֛יִם בַּחֹ֥דֶשׁ הָרִאשׁ֖וֹן לֵאמֹֽר׃

And the Lord spoke to Moshe in the wilderness of Sinay, in the first month of the second year after they were come out of the land of Miżrayim, saying,