To various governors concerning prayers
Nahj al-Balāgha|Volume 1|Book 2|Chapter 52
وَصَلُّوا بِهِمُ الْعِشَاءَ حِينَ يَتَوَارَى الشَّفَقُ إِلَى ثُلُثِ اللَّيْلِ.
Say the ‘ishā’ (night) prayers with them when twilight disappears and upto one third of the night.