Is it legal to use BMS textures?

I’m making a map for CSGO, which is Half life themed, and i need textures. I saw a guy using BMS textures, so the question is that is it legal to use BMS textures in another game?

Pose your question in Crowbar Collective’s Discord Channel

You can use them, but only for non-commercial purposes.

Founded in 2004, became one of the first online communities dedicated to Valve’s Source engine development. It is more famously known for the formation of Black Mesa: Source under the 'Leakfree Modification Team' handle in September 2004.