To prove that the statement of His servant Prahlāda Mahārāja was substantial — in other words, to prove that the Supreme Lord is present everywhere, even within the pillar of an assembly hall — the Supreme Personality of Godhead, Hari, exhibited a wonderful form never before seen. The form was neither that of a man nor that of a lion. Thus the Lord appeared in His wonderful form in the assembly hall.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स विक्रमन् पुत्रवधेप्सुरोजसा निशम्य निर्ह्रादमपूर्वमद्भुतम् । अन्तःसभायां न ददर्श तत्पदं वितत्रसुर्येन सुरारियूथपाः
sa vikraman putravadhepsurojasā niśamya nirhrādamapūrvamadbhutam | antaḥsabhāyāṃ na dadarśa tatpadaṃ vitatrasuryena surāriyūthapāḥ
SB 7.8.17