While mother Yaśodā was churning butter, Lord Kṛṣṇa, desiring to drink the milk of her breast, appeared before her, and in order to increase her transcendental pleasure, He caught hold of the churning rod and began to prevent her from churning.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तां स्तन्यकाम आसाद्य मथ्नन्तीं जननीं हरिः । गृहीत्वा दधिमन्थानं न्यषेधत्प्रीतिमावहन्
tāṃ stanyakāma āsādya mathnantīṃ jananīṃ hariḥ | gṛhītvā dadhimanthānaṃ nyaṣedhatprītimāvahan
SB 10.9.4