After the incarnation of the first puruṣa [Kāraṇārṇavaśāyī Viṣṇu], the mahat-tattva, or the principles of material creation, take place, and then time is manifested, and in course of time the three qualities appear. Nature means the three qualitative appearances. They transform into activities.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
कालाद्गुणव्यतिकरः परिणामः स्वभावतः । कर्मणो जन्म महतः पुरुषाधिष्ठितादभूत्
kālādguṇavyatikaraḥ pariṇāmaḥ svabhāvataḥ | karmaṇo janma mahataḥ puruṣādhiṣṭhitādabhūt
SB 2.5.22