SB 7.4.30

tasya daitya-pateḥ putrāś
 catvāraḥ paramādbhutāḥ
prahrādo ’bhūn mahāṁs teṣāṁ
 guṇair mahad-upāsakaḥ
Word for word: 
tasya — of him (Hiraṇyakaśipu); daitya-pateḥ — the King of the Daityas; putrāḥ — sons; catvāraḥ — four; parama-adbhutāḥ — very qualified and wonderful; prahrādaḥ — the one named Prahlāda; abhūt — was; mahān — the greatest; teṣām — of all of them; guṇaiḥ — with transcendental qualities; mahat-upāsakaḥ — being an unalloyed devotee of the Supreme Personality of Godhead.
Translation: 
Hiraṇyakaśipu had four wonderful, well-qualified sons, of whom the one named Prahlāda was the best. Indeed, Prahlāda was a reservoir of all transcendental qualities because he was an unalloyed devotee of the Personality of Godhead.
Purport: 

yasyāsti bhaktir bhagavaty akiñcanā
 sarvair guṇais tatra samāsate surāḥ

“In one who has unflinching devotional faith in Kṛṣṇa, all the good qualities of Kṛṣṇa and the demigods are consistently manifest.” (Bhāg. 5.18.12) Prahlāda Mahārāja is praised herein for having all good qualities because of worshiping the Supreme Personality of Godhead. Therefore, a pure devotee, who has no motives, has all good qualities, material and spiritual. If one is spiritually advanced, being a staunch, liberal devotee of the Lord, all good qualities are manifest in his body. On the other hand, harāv abhaktasya kuto mahad-guṇāḥ: if one is not a devotee, even if he has some materially good qualities, they have no value. That is the verdict of the Vedas.