SB 2.9.6

sa cintayan dvy-akṣaram ekadāmbhasy
 upāśṛṇod dvir-gaditaṁ vaco vibhuḥ
sparśeṣu yat ṣoḍaśam ekaviṁśaṁ
 niṣkiñcanānāṁ nṛpa yad dhanaṁ viduḥ
Synonyms: 
saḥ — he; cintayan — while thus thinking; dvi — two; akṣaram — syllables; ekadā — once upon a time; ambhasi — in the water; upāśṛṇot — heard it nearby; dviḥ — twice; gaditam — uttered; vacaḥ — words; vibhuḥ — the great; sparśeṣu — in the sparśa letters; yat — which; ṣoḍaśam — the sixteenth; ekaviṁśam — and the twenty-first; niṣkiñcanānām — of the renounced order of life; nṛpa — O King; yat — what is; dhanam — wealth; viduḥ — as it is known.
Translation: 
While thus engaged in thinking, in the water, Brahmājī heard twice from nearby two syllables joined together. One of the syllables was taken from the sixteenth and the other from the twenty-first of the sparśa alphabets, and both joined to become the wealth of the renounced order of life.
Purport: 

In Sanskrit language, the consonant alphabets are divided into two divisions, namely the sparśa-varṇas and the tālavya-varṇas. From ka to ma the letters are known as the sparśa-varṇas, and the sixteenth of the group is called ta, whereas the twenty-first letter is called pa. So when they are joined together, the word tapa, or penance, is constructed. This penance is the beauty and wealth of the brāhmaṇas and the renounced order of life. According to Bhāgavata philosophy, every human being is meant simply for this tapa and for no other business, because by penance only can one realize his self; and self-realization, not sense gratification, is the business of human life. This tapa, or penance, was begun from the very beginning of the creation, and it was first adopted by the supreme spiritual master, Lord Brahmā. By tapasya only can one get the profit of human life, and not by a polished civilization of animal life. The animal does not know anything except sense gratification in the jurisdiction of eat, drink, be merry and enjoy. But the human being is made to undergo tapasya for going back to Godhead, back home.

When Lord Brahmā was perplexed about how to construct the material manifestations in the universe and went down within the water to find out the means and the source of his lotus seat, he heard the word tapa vibrated twice. Taking the path of tapa is the second birth of the desiring disciple. The word upāśṛṇot is very significant. It is similar to upanayana, or bringing the disciple nearer to the spiritual master for the path of tapa. So Brahmājī was thus initiated by Lord Kṛṣṇa, and this fact is corroborated by Brahmājī himself in his book the Brahma-saṁhitā. In the Brahma-saṁhitā Lord Brahmā has sung in every verse govindam ādi-puruṣaṁ tam ahaṁ bhajāmi. Thus Brahmā was initiated by the Kṛṣṇa mantra, by Lord Kṛṣṇa Himself, and thus he became a Vaiṣṇava, or a devotee of the Lord, before he was able to construct the huge universe. It is stated in the Brahma-saṁhitā that Lord Brahmā was initiated into the eighteen-letter Kṛṣṇa mantra, which is generally accepted by all the devotees of Lord Kṛṣṇa. We follow the same principle because we belong to the Brahmā sampradāya, directly in the disciplic chain from Brahmā to Nārada, from Nārada to Vyāsa, from Vyāsa to Madhva Muni, from Madhva Muni to Mādhavendra Purī, from Mādhavendra Purī to Īśvara Purī, from Īśvara Purī to Lord Caitanya and gradually to His Divine Grace Bhaktisiddhānta Sarasvatī, our divine master.

One who is thus initiated in the disciplic succession is able to achieve the same result or power of creation. Chanting of this holy mantra is the only shelter of the desireless pure devotee of the Lord. Simply by such tapasya, or penance, the devotee of the Lord achieves all perfections like Lord Brahmā.