Yoga Sūtra Chapter Four verse 2

जात्यन्तरपरिणामः प्रकृत्यापूरातः ॥२॥

jāti-antara-pariṇāmaḥ prakṛti-āpūrāt ||2||

The transformation into other existences
is due to the flow from the process of matter.

jāti - existenceantara - otherpariṇāma - transformationprakṛti - process of matterāpūrā - flow