When King Bhagīratha approached Lord Śiva and requested him to sustain the forceful waves of the Ganges, Lord Śiva accepted the proposal by saying, “Let it be so.” Then, with great attention, he sustained the Ganges on his head, for the water of the Ganges is purifying, having emanated from the toes of Lord Viṣṇu.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
तथेति राज्ञाभिहितं सर्वलोकहितः शिवः । दधारावहितो गङ्गां पादपूतजलां हरेः
tatheti rājñābhihitaṃ sarvalokahitaḥ śivaḥ | dadhārāvahito gaṅgāṃ pādapūtajalāṃ hareḥ
SB 9.9.9