Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him) narrates that the Messenger of Allah (peace and blessings be upon him) used to pray four rak'ahs before Zuhr, when the sun passed the meridian. I said: O Messenger of Allah, what prayer is this? He (peace and blessings be upon him) said: "The gates of the heaven are opened when the sun passes the meridian and remain open until Zuhr is prayed, and I love that a righteous deed of mine should be raised up during (those moments)."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4016