Mundaka 1.01
brahmā devānāṃ prathamaḥ sambabhūva viśvasya kartā bhuvanasya goptā। sa brahmavidyāṃ sarvavidyāpratiṣṭhāṃ atharvāya jyeṣṭhaputrāya prāha ॥1॥
Brahma, the first of the gods, was born the creator and protector of the universe. He imparted the supreme knowledge of Brahman, which is the basis of all knowledge, to Atharva, his eldest son.
Bhāshya 1.01
A testimonial from Brahmāṇḍ Purāna explains how Shiva was first son of Lord Brahma in the first kalpa, while Atharva was the firs son in the Vaivasvata Manu kalpa.
manorvaivasvatasya'dāvatharvā brahmaṇo'jani। mitraśca varuṇaścātho prahetirhetireva ca। brahmaṇaḥ prathame kalpe śivaḥ prathamajaḥ sutaḥ। sanakādyāstu vārāhe brahmā viṣṇoḥ suto'grajaḥ॥
An the beginning of the reign of Vaivasvata Manu, Atharva was born from Brahma. Subsequently came Mitra and Varuna, followed by Praheti and Heti. In the first kalpa, Shiva was the firstborn son of Brahma. However, during the Varaha kalpa, Sanaka and others are considered firstborn sons, Brahma being the son of Lord Vishnu.
iti brahmāṇḍe।
- stated thus in the Brahmāṇḍ Purāna.
