Bhagavad Gita 10.35 Chapter 10, Verse 35

बृहत्साम तथा साम्नां गायत्री छन्दसामहम् ।
मासानां मार्गशीर्षोऽहमृतूनां कुसुमाकरः ॥१०.३५॥

bṛhatsāma tathā sāmnāṃ gāyatrī chandasāmaham
māsānāṃ mārgaśīrṣo'hamṛtūnāṃ kusumākaraḥ

Meaning

Among Sama hymns I am the Brihat Sama; among metres, the Gayatri; among months, Margashirsha; and among seasons, flower-bearing spring.

Newly written by Bhajan Dhun — scholarly review in progress.

Reference: Bhagavad Gita 10.35 (Chapter 10, The Yoga of Divine Glories (Vibhuti Yoga), Verse 35)