الْحَيَاءُ شُعْبَةٌ مِنَ الْإِيمَانِ.
Modesty is a branch of faith.
Source: al-Bukhari and Muslim (as cited in the book).
ArabicMeaning and grammar
الْحَيَاءُmodesty; an inner restraint from wrong
شُعْبَةٌa branch or part; indefinite predicate
مِنَ الْإِيمَانِof faith; مِنْ conveys being part of something
The relevant form of modesty restrains a person from shamelessness, injustice, cheating, and sin. It is not merely embarrassment in front of others: refusing to do wrong even when alone can express genuine haya. شُعْبَةٌ indicates an important part of faith, not the claim that faith consists of only this one quality.