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

(1) Lest ye should say: "The Book was sent down to two Peoples before us, and for our part, we remained unacquainted with all that they learned by assiduous study:"

(سورة الأنعام, Al-An'aam, Chapter #6, Verse #156)
(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) Behold! he said to his father and his people, "What are these images, to which ye are (so assiduously) devoted?"

(سورة الأنبياء, Al-Anbiyaa, Chapter #21, Verse #52)
(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)