Bamidbar 29:36

פר אחד איל אחד ONE BULLOCK, ONE RAM — these are an allusion to Israel who form one nation: “Stay with me a little longer”. And this conveys the idea of God’s affection for Israel — just like children who think to take leave of their father to whom he says, “Parting from you is very hard to me; stay one day more”. — A parable! It may be compared to the case of a king who made a banquet etc., as it is related in Treatise Sukkah 55b. And in the Midrash of R. Tanchuma 4:8:17 it states: The Torah teaches you a rule of conduct — that he who has a stranger staying with him should give him on the first day fattened poultry to eat, on the morrow he should give him fish to eat, on the next day animal flesh; on the following day he should give him pulse to eat, and on the next day vegetables, diminishing gradually, just as was the case with the bullocks on the Feast of Tabernacles.

וְהִקְרַבְתֶּ֨ם עֹלָ֜ה אִשֵּׁ֨ה רֵ֤יחַ נִיחֹ֙חַ֙ לַֽיהֹוָ֔ה פַּ֥ר אֶחָ֖ד אַ֣יִל אֶחָ֑ד כְּבָשִׂ֧ים בְּנֵי־שָׁנָ֛ה שִׁבְעָ֖ה תְּמִימִֽם׃

but you shall offer a burnt offering, a sacrifice made by fire, of a sweet savour to the Lord: one bullock, one ram, seven lambs of the first year without blemish: