ENOfficial
‘A'isha said that they used to pray the night prayer at any time after the ending of the twilight until a third of the night had passed. (Bukhari and Muslim)
Source: sunnah.com
Other translations
Arabic
وَعَنْ عَائِشَةَ رَضِيَ اللَّهُ عَنْهَا قَالَتْ: كَانُوا يُصَلُّونَ الْعَتَمَةَ فِيمَا بَيْنَ أَنْ يغيب لاشفق إِلَى ثلث اللَّيْل الأول
sunnah.com