Hiranyakeshigrihyasutra 1.2.5.10

1.2.5.10

savitā tvābhirakṣatu mitrastvamasi dharmaṇā \ agnirācāryastava \ devena savitrā prasūto bṛhaspaterbrahmacārī bhavāsāvapośānaḥ samidha ādhehi karma kuru mā divā svāpsīḥ \ ityenaṃ saṃśāsti \10\

'May Savitri protect thee. Mitra art thou by rights; Agni is thy teacher.
'By the impulse of the god Savitri become Brihaspati's pupil. Eat water. Put on fuel. Do the service. Do not sleep in the day-time'—thus (the teacher) instructs him.