Previous to the appearance of Lord Krsna, this original Sankarsana will appear as Baladeva, just to please the Supreme Lord Krsna in His transcendental pastimes - SB 10.1.24

Expressions researched:
"Previous to the appearance of Lord Kṛṣṇa, this original Saṅkarṣaṇa will appear as Baladeva, just to please the Supreme Lord Kṛṣṇa in His transcendental pastimes"

Srimad-Bhagavatam

SB Canto 10.1 to 10.13

Previous to the appearance of Lord Kṛṣṇa, this original Saṅkarṣaṇa will appear as Baladeva, just to please the Supreme Lord Kṛṣṇa in His transcendental pastimes.

SB 10.1.24, Translation and Purport

The foremost manifestation of Kṛṣṇa is Saṅkarṣaṇa, who is known as Ananta. He is the origin of all incarnations within this material world. Previous to the appearance of Lord Kṛṣṇa, this original Saṅkarṣaṇa will appear as Baladeva, just to please the Supreme Lord Kṛṣṇa in His transcendental pastimes.

Śrī Baladeva is the Supreme Personality of Godhead Himself. He is equal in supremacy to the Supreme Godhead, yet wherever Kṛṣṇa appears, Śrī Baladeva appears as His brother, sometimes elder and sometimes younger. When Kṛṣṇa appears, all His plenary expansions and other incarnations appear with Him. This is elaborately explained in Caitanya-caritāmṛta. This time, Baladeva would appear before Kṛṣṇa as Kṛṣṇa's elder brother.