O King, when the demigods and demons, by the strength of their arms, rotated Mandara Mountain on the back of the extraordinary tortoise, the tortoise accepted the rolling of the mountain as a means of scratching His body, and thus He felt a pleasing sensation.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
सुरासुरेन्द्रैर्भुजवीर्यवेपितं परिभ्रमन्तं गिरिमङ्ग पृष्ठतः । बिभ्रत्तदावर्तनमादिकच्छपो मेनेऽङ्गकण्डूयनमप्रमेयः
surāsurendrairbhujavīryavepitaṃ paribhramantaṃ girimaṅga pṛṣṭhataḥ | bibhrattadāvartanamādikacchapo mene'ṅgakaṇḍūyanamaprameyaḥ
SB 8.7.10