Bhagavad Gita 10.35
Of hymns, I am Brihatsama; of meters, I am Garatri; among months, I am Margasheersha (December); and I am Spring among seasons.
बृहत्साम तथा साम्नां गायत्री छन्दसामहम्।
मासानां मार्गशीर्षोऽहमृतूनां कुसुमाकरः॥bṛhatsāma tathā sāmnāṃ gāyatrī chandasāmaham|
māsānāṃ mārgaśīrṣo'hamṛtūnāṃ kusumākaraḥ||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).