Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 36
Sanskrit:
राजंश्चतुर्दशैतानि त्रिकालानुगतानि ते ।प्रोक्तान्येभिर्मित: कल्पो युगसाहस्रपर्यय: ॥ ३६ ॥
ITRANS:
rājaṁś caturdaśaitānitri-kālānugatāni teproktāny ebhir mitaḥ kalpoyuga-sāhasra-paryayaḥ
Translation:
O King, I have now described to you the fourteen Manus appearing in the past, present and future. The total duration of time ruled by these Manus is one thousand yuga cycles. This is called a kalpa, or one day of Lord Brahmā.