Numbers 7:3

שש עגלת צב SIX COVERED WAGGONS — The word צב means “covered over”. Similar is, (Isaiah 66:20) “(And they shall bring all your brethren …] in covered wagons (בצבים) and upon mules”, where covered wagons are called צבים without the addition of a word denoting “wagons” (Sifrei Bamidbar 46 1). ויקרבו אותם לפני המשכן AND THEY BROUGHT THEM BEFORE THE TABERNACLE — because Moses would not accept them (the gifts) at their (the princes’) hands until he was so bidden by the mouth of the Omnipresent (cf. v. 5). — Rabbi Nathan said: What reason had the princes to give their contributions here first of all the people, whereas at the work of the Tabernacle they were not the first but the last to contribute? But — he replied — the princes spoke thus: “Let the community in general contribute all they wish to give and then what will then be lacking we shall supply”. As soon as they saw that the community gave everything needed in its entirety (lit., that the community completed everything) — as it said, (Exodus 36:7) “For the stuff they had was enough [for all the work to make it]” — the princes asked, ‘What can we now do’? Therefore they brought the onyx stones, and stones for setting for the Ephod and for the breast plate. That is why they were here the first to contribute” (Sifrei Bamidbar 45 1).

and they brought their offering before the Lord, six covered wagons, and twelve oxen; a wagon for every two of the princes, and for each one an ox: and they brought them before the tabernacle.

וַיָּבִ֨יאוּ אֶת־קׇרְבָּנָ֜ם לִפְנֵ֣י יְהֹוָ֗ה שֵׁשׁ־עֶגְלֹ֥ת צָב֙ וּשְׁנֵ֣י עָשָׂ֣ר בָּקָ֔ר עֲגָלָ֛ה עַל־שְׁנֵ֥י הַנְּשִׂאִ֖ים וְשׁ֣וֹר לְאֶחָ֑ד וַיַּקְרִ֥יבוּ אוֹתָ֖ם לִפְנֵ֥י הַמִּשְׁכָּֽן׃