Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) said: "Every night, in the last third of it, Allah Almighty descends to the lowest heaven, and a caller announces: Is there anyone who asks so that I may grant him? Is there anyone seeking forgiveness so that I may forgive him? He says this three times."
Hadith Referenceمسند اسحاق بن راهويه / كتاب التهجد و التطوع / 235
Hadith Takhrij«بخاري ، كتاب التهجد ، باب الدعاء والصلاة الخ ، رقم : 1145 . مسلم ، كتاب صلاة المسافرين ، باب الترغيب فى الدعاء ، الخ ، رقم : 758»