Mbh 12.290.4a

"'Bhishma said, "In days of yore (having swallowed up Usanas), Mahadeva of severe vows entered the waters and remained there like an immovable stake of wood, O king, for millions of years (engaged in Yoga-meditation). His Yoga penances of the austerest type having been over, he rose from the mighty lake. Then that primeval god of the gods, viz., the eternal Brahman, approached him, and enquired after the progress of his penances and after his welfare. The deity having the bull for his emblem answered, saying, 'My penances have been well-practised.' Of inconceivable soul, possessed of great intelligence, and ever devoted to the religion of truth, Sankara saw that Usanas within his stomach had become greater in consequence of those penances of his.[1495] That foremost of Yogins (viz., Usanas), rich with that wealth of penances and the wealth (he had appropriated from Kuvera), shone brightly in the three worlds, endued with great energy.[1496] After this, Mahadeva armed with Pinaka, that soul of Yoga, once more betook himself to Yoga-meditation. Usanas, however, filled with anxiety, began to wander within the stomach of the great god. The great ascetic began to hymn the praises of the god from where he was, desirous of finding an outlet for escape. Rudra, however, having stopped all his outlets, prevented him from coming out. The great ascetic Usanas, however, O chastiser of foes, from within Mahadeva's stomach, repeatedly addressed the god, saying, 'Show me thy kindness!' Unto him Mahadeva said, 'Go out through my urethra.' He had stopped up all other outlets of his body. Confined on every side and unable to find out the outlet indicated, the ascetic began to wander hither and thither, burning all the while with Mahadeva's energy. At last he found the outlet and issued through it.