“فَ” (fa)This word resumes the flow after a pause or change in thought.Corpus grammarREM — prefixed rem particle.
“كَذَّبَ” (kadhkaba)means “But he denied” in this verse. It is a verb. an action or state word. Here it is perfect verb, verb pattern two, third person — masculine — singular.Corpus grammarV — third person masculine singular perfect verb.