The word(s) "unfaith" appears 2 time(s) in 2 verse(s) in Quran in Abdullah Yusuf Ali translation.

(1) But if they violate their oaths after their covenant, and taunt you for your Faith,- fight ye the chiefs of unfaith: for their oaths are nothing to them: that thus they may be restrained.

(سورة التوبة, At-Tawba, Chapter #9, Verse #12)
(Arabic, Transliteration, Urdu (Ahmed Ali), Urdu (Jalandhry), Farsi, Yusuf Ali, Shakir, Picthal, Mohsin Khan, French, Spanish, Indonesian, Malay, German, Bosnian, Russian, Dutch, Italian, Portuguese, Tafsir - Jalal ad-Din, Tafsir - King Fahad Quran Complex)

(2) Of Allah, to Whom do belong all things in the heavens and on earth! But alas for the Unbelievers for a terrible penalty (their unfaith will bring them)!-

(سورة ابراهيم, Ibrahim, Chapter #14, Verse #2)
(Arabic, Transliteration, Urdu (Ahmed Ali), Urdu (Jalandhry), Farsi, Yusuf Ali, Shakir, Picthal, Mohsin Khan, French, Spanish, Indonesian, Malay, German, Bosnian, Russian, Dutch, Italian, Portuguese, Tafsir - Jalal ad-Din, Tafsir - King Fahad Quran Complex)