"The Messenger of Allah (may Allah's peace and blessings be upon him) was asked:Which supplication is most likely to be answered?" He said: "A supplication made in the middle of the last part of the night and after conclusion of the obligatory prayers." [At-Tirmidhi]

"عن أبي أمامة -رضي الله عنه- مرفوعاً: قيل لرسول الله -صلى الله عليه وسلم-: أيُّ الدعاء أسمع؟ قال: «جَوْفَ الليل الآخِر، ودُبُر الصلوات المكتوبات». [حسن.] - [رواه الترمذي.]"