Vishnupurana 1.3.5

1.3.5

nijena tasya mānena āyurvarṣaśataṃ smṛtam /
tatparākhyaṃ tadarddha ca parārdhamabhidhiyate //

Brahmá is said to be born: a familiar phrase, to signify his manifestation; and, as the peculiar measure of his presence, a hundred of his years is said to constitute his life: that period is also called Param, and the half of it, Parárddham. I have already declared to you, oh sinless Brahman, that Time is a form of Vishńu: hear now how it is applied to measure the duration of Brahmá, and of all other sentient beings, as well as of those which are unconscious, as the mountains, oceans, and the like.