Sunan Abi Dawud Book 5, Hadith 112
The Messenger of Allah (ﷺ) offered the night prayer and then prayed eight rak'ahs standing, and two rak'ahs between the two adhans (i.e. the adhan for the dawn prayer and the iqamah). He never left them.
Jaf'ar b. Musafir said in his version: (He prayed) the two rak'ahs sitting between the two adhans. He added the word "sitting".
The Prophet (ﷺ) used to pray thirteen rak'ahs during the night including the two rak'ahs of the dawn prayer.
How many rak'ahs would the Messenger of Allah (ﷺ) pray observing the witr ? She said: He used to observe the witr with four and three, six and three, eight and three, and ten and three rak'ahs never observing less than seven or more than thirteen.
The narrator Ahmad added in his version: He would not observe the witr with two rak'ahs before the dawn. I asked: With what would he observe the witr ? She said: He would never leave it. The version of Ahmad does not mention the words "six and three (rak'ahs)".