Matthew 17:17ἄπιστος
“O unbelieving and perverse generation!” Jesus replied. “How long must I remain with you? How long must I put up with you? Bring the boy here to Me.”
Mark 9:19ἄπιστος
“O unbelieving generation!” Jesus replied. “How long must I remain with you? How long must I put up with you? Bring the boy to Me.”
Luke 9:41ἄπιστος
“O unbelieving and perverse generation!” Jesus replied. “How long must I remain with you and put up with you? Bring your son here.”
John 20:27ἄπιστος
Then Jesus said to Thomas, “Put your finger here and look at My hands. Reach out your hand and put it into My side. Stop doubting and believe.”
1 Corinthians 6:6ἀπίστων
Instead, one brother goes to law against another, and this in front of unbelievers!
2 Corinthians 4:4ἀπίστων
The god of this age has blinded the minds of unbelievers, so they cannot see the light of the gospel of the glory of Christ, who is the image of God.

Abbott-Smith

ἄ-πιστος, -ον
(ἀ- neg., πιστός) [in LXX: Pro.17:6 28:25, Isa.17:10 * ;]

(a) of things, incredible: Act.26:8;

(b) of persons, without faith or trust, unbelieving: Mat.17:17, Mrk.9:19, Luk.9:41 12:46, Jhn.20:27, Tit.1:15, Rev.21:8; specif., of unbelievers as opposite to Christians: 1Co.6:6 7:12-15 10:27 14:22-24, 2Co.4:4 6:14-15, 1Ti.5:8 (cf. Lft., Notes, 265; Cremer, 491).†
(AS)

Sources: Abbott-Smith’s Manual Greek Lexicon of the New Testament (1922, public domain) and glosses from STEPBible TBESG (CC BY 4.0); STEPBible TAGNT (Greek New Testament, CC BY 4.0); the Berean Standard Bible (public domain). Reformatted by Word Study, wording unchanged. All sources and licenses.