Sayyiduna Abu Ayyub (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) used to pray four rak'ahs before Zuhr. It was said to him (peace and blessings be upon him): "Do you keep up this prayer constantly?" He (peace and blessings be upon him) said: "When the sun passes its zenith, the gates of heaven are opened, and I love that my deeds go up before the gates of heaven are closed."
(b) The established (authentic) hadith has come permitting five rak'ahs in witr, with no tashahhud and no salam between them except in the last of them; and permitting nine, sitting only in the eighth and saying the salam only in the ninth. That too is mentioned in (the chapter of) witr.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4581