It is narrated from Sayyiduna Abu Ayyub al-Ansari (may Allah be pleased with him); he said: I said: O Messenger of Allah, what are these four rak'ahs? He (peace and blessings be upon him) said: "This is the hour in which the gates of the heaven are opened, and they are not closed until Zuhr is prayed, so I love to be ahead (in good deeds)."
Hadith Referenceالمعجم الكبير للطبراني / باب الخاء / 4021