Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 34

Sanskrit:

अपिस्विदास्ते भगवान् सुखं वोय: सात्वतां कामदुघोऽनिरुद्ध: ।यमामनन्ति स्म हि शब्दयोनिंमनोमयं सत्त्वतुरीयतत्त्वम् ॥ ३४ ॥

ITRANS:

apisvid āste bhagavān sukhaṁ voyaḥ sātvatāṁ kāma-dugho ’niruddhaḥyam āmananti sma hi śabda-yoniṁmano-mayaṁ sattva-turīya-tattvam

Translation:

May I inquire whether Aniruddha is doing well? He is the fulfiller of all the desires of the pure devotees and has been considered from yore to be the cause of the Ṛg Veda, the creator of the mind and the fourth plenary expansion of Viṣṇu.

Purport:

Ādi-caturbhuja, the original expansions from Baladeva, are Vāsudeva, Saṅkarṣaṇa, Pradyumna and Aniruddha. All of Them are viṣṇu-tattvas, or nondifferent Personalities of Godhead. In the incarnation of Śrī Rāma, all these different expansions appeared for particular pastimes. Lord Rāma is the original Vāsudeva, and His brothers were Saṅkarṣaṇa, Pradyumna and Aniruddha. Aniruddha is also the cause of Mahā-Viṣṇu, from whose breathing the Ṛg Veda appeared. All this is nicely explained in the Mārkaṇḍeya Purāṇa. In the incarnation of Lord Kṛṣṇa, Aniruddha appeared as the son of the Lord. Lord Kṛṣṇa in Dvārakā is the Vāsudeva expansion of the original group. The original Lord Kṛṣṇa never leaves Goloka Vṛndāvana. All the plenary expansions are one and the same viṣṇu-tattva, and there is no difference in Their potency.