CC Madhya 25.94

praṇavera yei artha, gāyatrīte sei haya
sei artha catuḥ-ślokīte vivariyā kaya
Word for word: 
praṇavera — of the sound vibration, oṁkāra; yei — whatever; artha — meaning; gāyatrīte — in the Gāyatrī mantra; sei — that; haya — there is; sei artha — that same meaning; catuḥ-ślokīte — in Śrīmad-Bhāgavatam summarized in four ślokas; vivariyā — describing elaborately; kaya — has said.
Translation: 
“The meaning of the sound vibration oṁkāra is present in the Gāyatrī mantra. The same is elaborately explained in the four ślokas of Śrīmad-Bhāgavatam known as the catuḥ-ślokī.