Valmiki Ramayana Aranya Kanda Sarga 16 Shloka 12
Original Shlokaनिवृत्ताकाशशयनाः पुष्यनीता हिमारुणाः। शीता वृद्धतरायामास्त्रियामा यान्ति साम्प्रतम्।।3.16.12।।
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साम्प्रतम् at this time, निवृत्ताकाशशयनाः sleep under the open sky, हिमारुणाः reddened due to frost, शीताः cool, वृद्धतरायामाः nights are long, पुष्यनीताः (the month of) Pushya approaching, त्रियामाः night consisting of three yamas (yama 3 hours approximately), यान्ति run into
At this time people do not sleep under the open sky. With the month of Pushya approaching, nights feel cool and look red due to frost. They prolong into three yamas.