Śukadeva Gosvāmī continued: Upon Lord Śiva’s drinking the poison, both the demigods and the demons, being very pleased, began to churn the ocean with renewed vigor. As a result of this, there appeared a cow known as surabhi.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
श्रीशुक उवाच । पीते गरे वृषाङ्केण प्रीतास्तेऽमरदानवाः । ममन्थुस्तरसा सिन्धुं हविर्धानी ततोऽभवत्
śrīśuka uvāca | pīte gare vṛṣāṅkeṇa prītāste'maradānavāḥ | mamanthustarasā sindhuṃ havirdhānī tato'bhavat
SB 8.8.1