Śrīmad-Bhāgavatam · Text 3.11.10
Who is speaking and story frame
यामाश्चत्वारश्चत्वारो मर्त्यानामहनी उभे ।
पक्ष: पञ्चदशाहानि शुक्ल: कृष्णश्च मानद ॥ १० ॥
yāmāś catvāraś catvāro
martyānām ahanī ubhe
pakṣaḥ pañca-daśāhāni
śuklaḥ kṛṣṇaś ca mānada
It is calculated that there are four praharas, which are also called yāmas, in the day and four in the night of the human being. Similarly, fifteen days and nights are a fortnight, and there are two fortnights, white and black, in a month.
Read this verse on Vedabase.ioThis verse has no purport; its meaning is explained by the verses around it.