This hadeeth comes under the following chapter: PRAYER DURING THE NIGHT AND THE NUMBER OF THE RAK'AHS WHICH THE APOSTLE (SALLALLAAHU ALAYHI WA SALLAM) OBSERVED IN THE NIGHT AND OBSERVANCE OF ONE RAKIAH OF WITR
'A'isha reported that the Messenger of Allaah (sallAllaahu alayhi wa sallam) used to pray eleven rak'ahs at night, observing the Witr with a single rak'ah, and when he had finished them, he lay down on his right side, till the Mu'adhdhin came to him and he (the Prophet) then observed two short rak'ahs (of Sunan of the dawn prayer).