Ūṣā, the wife of Vibhāvasu, gave birth to three sons — Vyuṣṭa, Rociṣa and Ātapa. From Ātapa came Pañcayāma, the span of day, who awakens all living entities to material activities.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
विभावसोरसूतोषा व्युष्टं रोचिषमातपम् । पञ्चयामोऽथ भूतानि येन जाग्रति कर्मसु
vibhāvasorasūtoṣā vyuṣṭaṃ rociṣamātapam | pañcayāmo'tha bhūtāni yena jāgrati karmasu
SB 6.6.16