Abdullah bin Umar used to say the salam between the second and third units of the witr prayer, even giving instructions about some of his needs in between.
Bukhari 991
Sahih
و
عن نافع
أن عبد الله بن عمر كان يسلم بين الركعة والركعتين في الوتر حتى يأمر ببعض حاجته