Shiva Purana
अगर्भाद्गर्भसंयुक्तः प्राणायामःशताधिकः ॥ तस्मात्सगर्भं कुर्वन्ति योगिनः प्राणसंयमम् ॥ ३४ ॥
The Sagarbha Prāṇāyāma is hundred times more efficacious than the Agarbha. Yogins practise Sagarbha Prāṇāyāma.
english translation
agarbhAdgarbhasaMyuktaH prANAyAmaHzatAdhikaH ॥ tasmAtsagarbhaM kurvanti yoginaH prANasaMyamam ॥ 34 ॥
hk transliteration by Sanscript