Srimad-Bhagavatam: Canto 4 - Chapter 1 - Verse 76
Sanskrit:
पञ्चमे मास्यनुप्राप्ते जितश्वासो नृपात्मज: ।ध्यायन् ब्रह्म पदैकेन तस्थौ स्थाणुरिवाचल: ॥ ७६ ॥
ITRANS:
pañcame māsy anuprāptejita-śvāso nṛpātmajaḥdhyāyan brahma padaikenatasthau sthāṇur ivācalaḥ
Translation:
By the fifth month, Mahārāja Dhruva, the son of the King, had controlled his breathing so perfectly that he was able to stand on only one leg, just as a column stands, without motion, and concentrate his mind fully on the Parabrahman.