Abu Umamah (May Allah be pleased with him) reported:
The Messenger of Allah ﷺ was asked: "At what time does the supplication find the greatest response?" He ﷺ replied, "A supplication made during the middle of the last part of the night and after the conclusion of the obligatory prayers."

[At-Tirmidhi].

وعن أبي أمامة رضي الله عنه قال: قيل لرسول الله ﷺ: أي الدعاء أسمع؟ قال: "جوف الليل الآخر ودبر الصلوات المكتوبات". رواه الترمذي وقال حديث حسن.