Abdullah bin Abi Qays says: I said to Sayyidah Aishah (may Allah be pleased with her): How many (rak'ahs) was the witr of the Prophet (peace and blessings be upon him)? She said: He (peace and blessings be upon him) prayed four and three, six and three, eight and three, ten and three, and he did not pray fewer than seven witr, nor more than thirteen. Ahmad (may Allah have mercy on him) added: He (peace and blessings be upon him) did not pray witr with the two rak'ahs of Fajr. I said: How was his (peace and blessings be upon him) witr? She said: He (peace and blessings be upon him) never left it. Ahmad (may Allah have mercy on him) did not mention the words "six and three". It is possible that what is meant is that he (peace and blessings be upon him) prayed three witr, neither sitting nor saying the salam in between, so it would carry the meaning of the narration of Hisham bin Urwah (may Allah have mercy on him).
(b) A narration with the same meaning as the narration of Hisham bin Urwah (may Allah have mercy on him) about five rak'ahs of witr has also been reported from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) from the Prophet (peace and blessings be upon him).
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4804