Srimad-Bhagavatam: Canto 9 - Chapter 1 - Verse 2
Sanskrit:
तस्यापि भगवानेष साक्षाद् ब्रह्ममयो हरि: ।अंशांशेन चतुर्धागात् पुत्रत्वं प्रार्थित: सुरै: ।रामलक्ष्मणभरतशत्रुघ्ना इति संज्ञया ॥ २ ॥
ITRANS:
tasyāpi bhagavān eṣasākṣād brahmamayo hariḥaṁśāṁśena caturdhāgātputratvaṁ prārthitaḥ suraiḥrāma-lakṣmaṇa-bharata-śatrughnā iti saṁjñayā
Translation:
Being prayed for by the demigods, the Supreme Personality of Godhead, the Absolute Truth Himself, directly appeared with His expansion and expansions of the expansion. Their holy names were Rāma, Lakṣmaṇa, Bharata and Śatrughna. These celebrated incarnations thus appeared in four forms as the sons of Mahārāja Daśaratha.
Purport:
Lord Rāmacandra and His brothers, Lakṣmaṇa, Bharata and Śatrughna, are all viṣṇu-tattva, not jīva-tattva. The Supreme Personality of Godhead expands into many, many forms. Advaitam acyutam anādim ananta-rūpam. Although they are one and the same, viṣṇu-tattva has many forms and incarnations. As confirmed in the Brahma-saṁhitā (5.39), rāmādi-mūrtiṣu kalā-niyamena tiṣṭhan. The Lord is situated in many forms, such as Rāma, Lakṣmaṇa, Bharata and Śatrughna, and these forms may exist in any part of His creation. All these forms exist permanently, eternally, as individual Personalities of Godhead, and they resemble many candles, all equally powerful. Lord Rāmacandra, Lakṣmaṇa, Bharata and Śatrughna, who, being viṣṇu-tattva, are all equally powerful, became the sons of Mahārāja Daśaratha in response to prayers by the demigods.