The Prashna Upanishad with Shankara’s Commentary
अथैकयोर्ध्व उदानः पुण्येन पुण्यं लोकं नयति पापेन पापमुभाभ्यामेव मनुष्यलोकम् ॥ ७ ॥
athaikayordhva udānaḥ puṇyena puṇyaṃ lokaṃ nayati pāpena pāpamubhābhyāmeva manuṣyalokam || 7 ||
7. Now by one nerve, udâna ascending, conducts to virtuous worlds by virtue, to sinful worlds by sin and to the world of men by virtue and sin combined.
Com.—By one of these hundred and one nerves, i.e., by that nerve named sushumna which goes up, udâna moving in all portions, from the foot to the head, conducts one to virtuous worlds, such as the abode of the Dêvâs by virtuous deeds enjoined by the sâstrâs; by sinful deeds contrary to virtue, to sinful worlds, such as birth among horizontal creatures, i.e., beasts. By both equally combined, i.e., virtue and sin, to the world of men. ‘Conducts’ should be supplied.