SB 7.12.2

sāyaṁ prātar upāsīta
 gurv-agny-arka-surottamān
sandhye ubhe ca yata-vāg
 japan brahma samāhitaḥ
Word for word: 
sāyam — in the evening; prātaḥ — in the morning; upāsīta — he should worship; guru — the spiritual master; agni — the fire (by a fire sacrifice); arka — the sun; sura-uttamān — and Lord Viṣṇu, Puruṣottama, the best of personalities; sandhye — morning and evening; ubhe — both; ca — also; yata-vāk — without talking, being silent; japan — murmuring; brahma — the Gāyatrī mantra; samāhitaḥ — being fully absorbed.
Translation: 
At both junctions of day and night, namely, in the early morning and in the evening, he should be fully absorbed in thoughts of the spiritual master, fire, the sun-god and Lord Viṣṇu and by chanting the Gāyatrī mantra he should worship them.