Shiva Purana
कालो निशीथो वै प्रोक्तोमध्ययामद्वयं निशि । शिवपूजा विशेषेण तत्कालेऽभीष्टसिद्धिदा ६५ ।
The two middle Yāmas (1 Yāma is equal to 3 hours) at night are called Niśītha. The worship of Śiva at that time accords desired results.
english translation
kAlo nizItho vai proktomadhyayAmadvayaM nizi । zivapUjA vizeSeNa tatkAle'bhISTasiddhidA 65 ।
hk transliteration by Sanscript