Shiva Purana
निशांत्यायामोषा ज्ञेया यामार्धं संधिरुच्यते । तत्काले तु समुत्थाय विण्मूत्रे विसृजेद्द्विजः ९ ।
The last yāma (3 hours) of the night is called Uṣā and the latter half of it is sandhi (period of conjunction). A brahmin shall get up at that hour and answer the calls of nature.
english translation
nizAMtyAyAmoSA jJeyA yAmArdhaM saMdhirucyate । tatkAle tu samutthAya viNmUtre visRjeddvijaH 9 ।
hk transliteration by Sanscript