Canto 1, chapter 3 - Kṛṣṇa is the Source of all Incarnations

The third chapter of the first book, or Canto, of the Bhāgavata Purāṇa, also called the Śrīmad Bhāgavatam. It was written by the Vedic sage Śrī Kṛṣṇa Dvaipāyana Vyāsadeva and is about the life and times of Śrī Kṛṣṇa, the most renown avatar of India who spoke the Bhagavad Gītā. Text at: http://bhagavata.org/canto1/chapter3.html