CC Madhya 20.310
sañjāyate na tu tataḥ pṛthag asti hetoḥ
yaḥ śambhutām api tathā samupaiti kāryād
govindam ādi-puruṣaṁ tam ahaṁ bhajāmi
kṣīram — milk; yathā — as; dadhi — yogurt; vikāra-viśeṣa — with a special transforming agent; yogāt — by mixing; sañjāyate — is transformed into; na — not; tu — but; tataḥ — from the milk; pṛthak — separated; asti — is; hetoḥ — which is the cause; yaḥ — who; śambhutām — the nature of Lord Śiva; api — even though; tathā — as; samupaiti — accepts; kāryāt — for the matter of some particular business; govindam — unto Govinda, the Supreme Personality of Godhead; ādi-puruṣam — the original person; tam — unto Him; aham — I; bhajāmi — offer my respectful obeisances.
“ ‘Milk changes into yogurt when mixed with a yogurt culture, but actually it is constitutionally nothing but milk. Similarly, Govinda, the Supreme Personality of Godhead, assumes the form of Lord Śiva [Śambhu] for the special purpose of material transactions. I offer my obeisances at His lotus feet.’
This is a quotation from the Brahma-saṁhitā (5.45).