Where does “巴石” come from?

巴石 (Chinese) comes from Tagalog Pasig, from Proto-Malayo-Polynesian *pasiʀ.

Ancestry of “巴石”, step by step

Step	Language	Word	Meaning
1	Tagalog	Pasig	sandy riverbank
2	Proto-Malayo-Polynesian	*pasiʀ	—