Srimad-Bhagavatam: Canto 7 - Chapter 1 - Verse 2
Sanskrit:
स तेपे मन्दरद्रोण्यां तप: परमदारुणम् ।ऊर्ध्वबाहुर्नभोदृष्टि: पादाङ्गुष्ठाश्रितावनि: ॥ २ ॥
ITRANS:
sa tepe mandara-droṇyāṁtapaḥ parama-dāruṇamūrdhva-bāhur nabho-dṛṣṭiḥpādāṅguṣṭhāśritāvaniḥ
Translation:
In the valley of Mandara Hill, Hiraṇyakaśipu began performing his austerities by standing with his toes on the ground, keeping his arms upward and looking toward the sky. This position was extremely difficult, but he accepted it as a means to attain perfection.