Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 8
Sanskrit:
लघूनि वै समाम्नाता दश पञ्च च नाडिका ।ते द्वे मुहूर्त: प्रहर: षड्याम: सप्त नृणाम् ॥ ८ ॥
ITRANS:
laghūni vai samāmnātādaśa pañca ca nāḍikāte dve muhūrtaḥ praharaḥṣaḍ yāmaḥ sapta vā nṛṇām
Translation:
Fifteen laghus make one nāḍikā, which is also called a daṇḍa. Two daṇḍas make one muhūrta, and six or seven daṇḍas make one fourth of a day or night, according to human calculation.