The seven musical notes — ṣa, ṛ, gā, ma, pa, dha and ni — are used in musical instruments, but originally they come from the Sāma Veda. The great sage Nārada vibrates sounds describing the pastimes of the Supreme Lord. By such transcendental vibrations, such as Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare, he fixes his mind at the lotus feet of the Lord. Thus he directly perceives Hṛṣīkeśa, the master of the senses. After delivering the Haryaśvas, Nārada Muni continued traveling throughout the planetary systems, his mind always fixed at the lotus feet of the Lord.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
स्वरब्रह्मणि निर्भातहृषीकेशपदाम्बुजे । अखण्डं चित्तमावेश्य लोकाननुचरन् मुनिः
svarabrahmaṇi nirbhātahṛṣīkeśapadāmbuje | akhaṇḍaṃ cittamāveśya lokānanucaran muniḥ
SB 6.5.22