Musnad Abu Ya'la al-Mawsili 209:85

Abu Khaythama narrated to us, Jarir narrated to us, from Mansur, from al-Hakam, from Miqsam, from Umm Salamah, who said: The Messenger of Allah (may Allah bless him and grant him peace) used to perform Witr with seven or five [rak'ahs], not separating between them with a taslim or speech.