Srimad-Bhagavatam: Canto 7 - Chapter 1 - Verse 10
श्रीनारद उवाचअयं निष्किल्बिष: साक्षान्महाभागवतो महान् ।त्वया न प्राप्स्यते संस्थामनन्तानुचरो बली ॥ १० ॥
śrī-nārada uvācaayaṁ niṣkilbiṣaḥ sākṣānmahā-bhāgavato mahāntvayā na prāpsyate saṁsthāmanantānucaro balī
Nārada Muni replied: The child within this woman’s womb is faultless and sinless. Indeed, he is a great devotee, a powerful servant of the Supreme Personality of Godhead. Therefore you will not be able to kill him.
There have been many instances in which demons or nondevotees have attempted to kill a devotee, but they have never been able to destroy a great devotee of the Supreme Personality of Godhead. The Lord promises in Bhagavad-gītā (9.31), kaunteya pratijānīhi na me bhaktaḥ praṇaśyati. This is a declaration by the Supreme Personality of Godhead that His devotee cannot be killed by demons. Prahlāda Mahārāja is the vivid example of the truth of this promise. Nārada Muni told the King of heaven, “It would be impossible for you to kill the child, even though you are demigods, and certainly it would be impossible for others.”