Exode 38:8

And he made the brasen Laver, and its foundation of brass, from the brasen mirrors of the pious women, who, at the season, came to pray at the door of the tabernacle of appointment, standing with their oblations, giving thanks and confession, and returning to their husbands, the mothers of righteous children, who had been purified from the uncleanness of their blood.

From the mirrors of the women who gathered. It was usual for women then as now to beautify themselves in front of a mirror in the morning. But there were some pious women who renounced worldly vanities and donated their copper mirrors for the making of the holy vessels. These women would gather every day near the entrance to the Tent of Meeting to pray and receive instruction in the commandments.

OF THE MIRRORS ‘HATZOVOTH’ (OF THE SERVING WOMEN). “The women of Israel possessed mirrors of brass which they used to look into when they adorned themselves, and even these they did not withhold [from donating to the Tabernacle]. But Moses was reluctant to accept them because they were made to arouse sensual desires. Said the Holy One, blessed be He, to Moses: ‘These are dearer to Me than all [other donations], for by means of them the women raised many hosts in Egypt, etc. For this reason the laver was made from these mirrors, because it was used in order to bring peace between husband and wife; for it was out of this laver that they took the water which they give to drink to a woman who was warned by her husband not to meet a certain man privately and who had nevertheless associated with him.” This is Rashi’s language.
The meaning of this Midrash is that in the whole work of the Tabernacle they accepted ornaments from women, as it is written, And they came, both men and women… and brought nose-rings, and ear-rings, and signet-rings ‘v’chumaz’ — the chumaz, according to its Midrashic interpretation, being even more undesirable. is explained as an ornament worn by women on their pudendum. There, however, all the donations became mixed together, whereas here they were to make one specific vessel purely from ornaments [i.e., the mirrors] which were made to arouse sensual desire. Therefore Moses did not consent at first [to accept them] until he was told to do so by the Almighty.
But I do not know how to explain according to this Midrash the phrase — that did service at the door of the Tent of Meeting — [since the Tent of Meeting had not yet been put up]. Perhaps it can be said that the women brought this donation to Moses’ tent, which he called the Tent of Meeting, and he himself received it from them by word of G-d, since the tent of the Tabernacle had not yet been made. Onkelos’ translation, “women that came to pray at the door of the Tent of Meeting,” accords approximately to the words of Rabbi Abraham ibn Ezra, who said that these women worshipped G-d, and turned away from the desires of this world and gave their mirrors as a donation, coming each day to the door of the Tent of Meeting to pray and to hear instruction about the commandments.
In line with the plain meaning of Scripture, it is also possible to say that Moses made the laver and its base for the mirrors of the women who came in a great crowd, as being from the root tzava (a host). Of the mirrors ‘hatzovoth’ would thus mean “of the mirrors of the hosts of women” who assembled at the door of the Tent of Meeting. and assembled at the door of the Tent of Meeting in order to give their mirrors in the generosity of their hearts. Now the brass of the mirrors was burnished brass, resplendent and very beautiful. It is for this reason that he set aside this brass from the beginning for the making of this vessel. Upon seeing this [that Moses accepted it from them], the women gathered and came in many hosts, all of them wanting to give their mirrors for the making of the whole laver and its base. It is also correct to explain that they had in mind right at the start to offer them for the laver because of its use in connection with the suspected adulteress [as explained above], and they accepted the law [of the suspected adulteress] upon themselves with joy, and offered to give all their mirrors.
Pekudei

במראות הצובאות, this was not included in the נחושת התנופה, “copper for the waving,” as explained in verse 30 of this chapter in Parshat Pekudey. The copper basin and its stand are mentioned as having been constructed from the amount of copper representing these mirrors.

אשר צבאו פתח אהל מועד, approaching this holy domain was intended to show that they wanted to hear the words of the living G’d. That this was an acceptable practice is already documented in 33,7 והיה כל מבקש ה' יצא אל אהל מועד, “anyone who wanted to seek out the Lord would go out to the Tent of Meeting.” The women who had donated these mirrors indicated that they had overcome their sense of vanity, they considered jewelry and the need for it a human weakness. Moreover, they knew that the time when these mirrors had been of constructive use was past.

במראות הצובאות, “with the mirrors of the serving women.” Moses placed the washbasin between the Tabernacle and the Altar (a bit to the north) as he wished that the women who were situated in front of the entrance to the Tabernacle could observe it. Moses wanted the women to be able to see the washbasin that the Sotah (woman suspected of infidelity) would be made to drink in order to prove that she was innocent of that sin.