Bhṛgu–Bharadvāja-saṃvāda: Vānaprastha-parivrājaka-ācāra, Abhaya-dharma, and Lokānāṃ Vibhāga (Śānti-parva 185)
तत्रैकगुणमाकाशं शब्द इत्येव तत्स्मृतम् । तस्य शब्दस्य वक्ष्यामि विस्तरं विविधात्मकम्
tatraikaguṇam ākāśaṃ śabda ity eva tat smṛtam | tasya śabdasya vakṣyāmi vistaraṃ vividhātmakam | eṣa saptavidhaḥ prokto guṇa ākāśasambhavaḥ |
तत्रैकगुणमाकाशं शब्द इत्येव तत्स्मृतम्। तस्य शब्दस्य वक्ष्यामि विस्तरं विविधात्मकम्॥ एष सप्तविधः प्रोक्तो गुण आकाशसम्भवः—षड्ज ऋषभ गान्धार मध्यम पञ्चम धैवत निषाद इति॥
भरद्वाज उवाच
Space (ākāśa) is characterized by a single fundamental attribute—sound (śabda). That one attribute is then analyzed as having a structured, sevenfold manifestation, commonly understood as the seven musical notes (saptasvara).
Bharadvāja is teaching a philosophical account of the elements and their qualities. In this verse he identifies the defining quality of ākāśa as sound and announces a detailed explanation of sound’s differentiated forms, presented as seven kinds.