God [is] faithful, by whom ye were called unto the fellowship of his Son Jesus Christ our Lord.
Berean Study Bible (BSB) - 1 Corinthians 1:9 >God, who has called you into fellowship with His Son Jesus Christ our Lord, is faithful.
Textus Receptus (TR) - 1 Corinthians 1:9 >Πιστὸς ὁ Θεός, δι᾿ οὗ ἐκλήθητε εἰς κοινωνίαν τοῦ υἱοῦ αὐτοῦ Ἰησοῦ Χριστοῦ τοῦ Κυρίου ἡμῶν.