The Prophet ﷺ used to separate the witr from the preceding pair of rakahs with a tasleem, letting us hear it.
كان النبي ﷺ يفصل بين الوتر والشفع بتسليمة ويسمعنا.
Imam Ahmad (5461) and Tabarani in al-Awsat (757) both narrated it through the hadith of Itaab bin Ziyad, who said, Abu Hamza, meaning Sukkari, narrated to us, from Ibrahim, meaning al-Sayigh, from Nafi, from Ibn Umar, and he related it. Ibn Hibban graded it sahih (2435) and narrated it through the route of Itaab bin Ziyad, with the same wording.Itaab bin Ziyad was deemed reliable by Abu Hatim and Ibn Saad, and he is truthful, one of the narrators found in Ibn Majah. Abu Hamza Sukkari's name is Muhammad bin Maymun, and he is reliable and virtuous, one of the narrators found in the major collections. Ibrahim al-Sayigh is Ibrahim bin Maymun al-Sayigh al-Marwazi, deemed reliable by Ibn Main and Nasai, and his hadith is hasan. Abu Dawud and Nasai narrated from him, and Bukhari narrated from him with a suspended chain.Hafiz Haythami said in al-Majma (2/243), after attributing it to Tabarani in al-Awsat alone, "It contains Ibrahim bin Saeed, who is daif."I say, it is not as he thought, may Allah have mercy on him, rather he is Ibrahim bin Maymun al-Sayigh. As for Ibrahim bin Saeed al-Madani, his hadith is rejected, as the author of al-Mizan said.The second observation is that Hafiz Haythami fell short by attributing it only to Tabarani, and he failed to attribute it to Imam Ahmad as well.This hadith attributed to the Prophet is strengthened by the practice of Ibn Umar, the narrator of the hadith, who was among the most rigorous of people in following the Prophet's example, for he used to give the taslim between one rakat and two rakats during Witr, even to the point of giving some instructions about his affairs. Malik narrated this in the chapter on Night Prayer (20), and through his route Bukhari narrated it in the chapter on Witr (991), from Nafi, from him.Saeed bin Mansur narrated with a sahih chain from Bakr bin Abdullah Muzani, who said, Ibn Umar prayed two rakats, then said, "Boy, saddle up for us," then he stood and prayed Witr with one rakat. See Fath al-Bari (2/482). Abu Bakr Ibn Abu Shayba likewise narrated this (2/292) through the route of Bakr bin Abdullah Muzani, with the same wording.