Sunan Abi Dawud 1093
سنن أبي داود#1093SahihJabir b. Samurah said:The Messenger of Allah (ﷺ) used to deliver the sermon standing, then he would sit down, then stand and preach standing. If anyone tells you he preached sitting, he is lying. I swear by Allah that I offered along with more than two thousand prayers
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniHasan
Muhammad Muhyi Al-Din Abdul HamidHasan
Shuaib Al ArnautSahih Lighairihi
Zubair Ali ZaiSahih Muslim (862)
In-book reference: 2:704