Sunan Abi Dawud 1358
سنن أبي داود#1358SahihSa'id b. Jubair said that Ibn 'Abbas told him:He (the Prophet) got up and prayed eight rak'ahs in pairs, and then observed witr with five rak'ahs and he did not sit between them
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Muhyi Al-Din Abdul HamidSahih
Zubair Ali ZaiIsnaad Sahih
In-book reference: 5:109