In Mahabharata, Santi Parva, SECTION XCVIII, it is said by Indra himself that he has slain Prahlada.
Having slain in battle Jambha, Vritra, Vala, Paka, Satamaya, Virochana, the irresistible Namuchi, Samvara of innumerable illusions, Viprachitti,--all these sons of Diti and Danu, as also Prahlada, I myself have become the chief of the celestials.'
48 अहं वृत्रं बलं पाकं शतमायं विरॊचनम
दुरावार्यं च नमुचिं नैकमायं च शम्बरम
49 विप्रचित्तिं च दैतेयं दनॊः पुत्राश च सर्वशः
परह्रादं च निहत्याजौ ततॊ देवाधिपॊ ऽभवम
50 इत्य एतच छक्र वचनं निशम्य परतिगृह्य च
यॊधानाम आत्मनः सिद्धिम अम्बरीषॊ ऽभिपन्नवान
48 ahaṃ vṛtraṃ balaṃ pākaṃ śatamāyaṃ virocanam
durāvāryaṃ ca namuciṃ naikamāyaṃ ca śambaram49 vipracittiṃ ca daiteyaṃ danoḥ putrāś ca sarvaśaḥ
prahrādaṃ ca nihatyājau tato devādhipo 'bhavam50 ity etac chakra vacanaṃ niśamya pratigṛhya ca
yodhānām ātmanaḥ siddhim ambarīṣo 'bhipannavān
So, I want to know why and when Prahlada was slain by Indra? Was he the same Prahlada (son of Hiranyakashipu) or someone else?
prahrāda ca nihan āji tatas deva adhipa bhū
. Please check the details by clicking on that line here