Sayyiduna Murrah bin Ka'b al-Bahzi (may Allah be pleased with him) said: I said: O Messenger of Allah! Which part of the night is most heard (for supplication)? He (peace and blessings be upon him) said: "The last middle part of the night; at that time prayer is accepted until dawn (Fajr) breaks. Then no prayer is offered until the sun has risen the height of one or two spears. Then prayer continues to be accepted until the shadow stands equal to the spear. Then there is no prayer until the sun passes its zenith. Then prayer continues to be accepted until the sun is the height of one or two spears before setting. Then there is no prayer until the sun sets."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17888