Is it Sunnah to wash new clothes before wearing them?

It is recommended in the prophetic Sunnah to offer supplication when putting on new clothes, so the Muslim should say: “Allahumma laka al-hamd, anta kasawtanihi, as-aluka min khayrihi wa khayri ma suni‘a lah, wa a‘udhu bika min sharrihi wa sharri ma suni‘a lah (O Allah, to You be praise, You have clothed me with it. I ask you for its good and the good of that for which it was made, and I seek refuge in You from its evil and the evil of that for which it was made).” Narrated by Ahmad (11248) and Abu Dawud (4520); classed as sahih by al-Albani in Sahih al-Jami‘ (4664).

This has been discussed previously in the answer to question no. 139146 .

As for washing new clothes before wearing them, we do not know of anything in the Sunnah to indicate that it is recommended to do that, and we do not know of anyone among the earlier generations or the scholars who recommended doing that or advised doing it.

But it may be advisable from a medical point of view, because doctors advise that it is essential to wash new clothes before wearing them, especially underwear and children’s clothes, because of bacteria or chemical contaminants that may have got onto them.

There is nothing wrong with that, if it is proven to be of benefit. Islamic teachings do not disallow that, because Islam brought general principles that advise maintaining good physical health and cleanliness.

And Allah knows best.