Syntax of fātahu al-wuqūf

Bab al-Fawat — Missing Hajj, Release, Makeup Hajj and Umrah

Fātahu al-wuqūfu bi-ʿArafah
Fāta: perfect verb.
-hu: attached object pronoun.
Al-wuqūfu: nominative subject of the verb, the thing missed.
Bi-ʿArafah: prepositional phrase specifying the site.

The suffix -hu is not the grammatical subject; al-wuqūf is.