2 Corinthians 4:13
We having the same spirit of faith, according as it is written, I believed, and therefore have I spoken; we also believe, and therefore speak;
Cross-reference
2 Corinthians 3:12
Parallel
In 2 Corinthians 3:12, hope produces boldness — parallel to faith producing speech here, both expressing confidence in God.
2 Corinthians 1:9
Parallel
In 2 Corinthians 1:9, Paul relies on God who raises the dead — the same faith that fuels the bold speaking in 4:13.
Psalm 116:10
Citation
Psalm 116:10 is the exact source Paul quotes — the psalmist's belief-led speech becomes his model of faith.
Hebrews 11:1
Related theme
Hebrews 11 defines and exemplifies the faith that believes and speaks — the same spirit of faith Paul invokes here.