Anandakanda 1.2.95

1.2.95

kūrmarūpī tu bhagavān devatā parikīrtitā /
pṛthvi tvayā dhṛtā lokā devi tvaṃ viṣṇunā dhṛtā /
tvaṃ ca dhāraya māṃ devi pavitraṃ kuru cāsanam /
anenaiva tu mantreṇa cāsane kusumaṃ kṣipet //

The Blessed One who has the form of a tortoise is proclaimed the deity:
'O Earth, the worlds are held by you; O goddess, you are held by Viṣṇu;
and do you hold me, O goddess, and make my seat pure.'
With this very mantra one should cast a flower onto the seat.