Acts 9:20

and immediately he began to proclaim Jesus in the synagogues, ¹  saying, “This man is the Son of God.” ² 

Ps 2:7,12; Mt 26:63-66; Mt 27:43,54; Joh 1:49; Joh 19:7; Joh 20:28,31; Ac 8:37; Ac 9:27,28; Ro 1:4; Ga 1:23,24; Ga 2:20; 1Jo 4:14,15; Re 2:18

¹ sn See the note on synagogue in 6:9.

² tn The ὅτι (Joti) is understood to introduce direct (“This man is the Son of God”) rather than indirect discourse (“that this man is the Son of God”) because the pronoun οὗτος (Jouto") combined with the present tense verb ἐστιν (estin) suggests the contents of what was proclaimed are a direct (albeit summarized) quotation.

sn This is the only use of the title Son of God in Acts. The book prefers to allow a variety of descriptions to present Jesus.