Skandapurana 3.3.2.8

3.3.2.8

māghe kṛṣṇacaturddaśyāmupavāso'ti durlabhaḥ..
tatrāpi durlabhaṃ manye rātrau jāgaraṇaṃ nṛṇām .. 8..

In the month of Māgha, on the fourteenth day of the dark fortnight, fasting is exceedingly rare; / even more difficult than that, I think, is the keeping of a night vigil by men.