Shiva Purana
ज्ञेयं पित्र्यमहोरात्रं मासः कृष्णसितात्मकः ॥ ६ ॥
The month consisting of black and white is to be understood as the day and night of the fathers.
english translation
jJeyaM pitryamahorAtraM mAsaH kRSNasitAtmakaH ॥ 6 ॥
hk transliteration by Sanscript