Sunan Abi Dawud Book 2, Hadith 410
We thought that by this (prolonging the first rak’ah). He (the prophet) meant that the people might join the first rak’ah.
He would recite Fatihat al-kitab in the last two surahs. Hammam added: He would prolong the first rak’ah but would not prolong the second so much; and he did so similarly in the afternoon prayer, and so in the morning prayer.
We asked Khabbab: Did the Messenger of Allah (ﷺ) recit (the Quran) in the noon and afternoon prayers? He replied: Yes. We then asked: How did you know this? He said: By the shaking of his beard, may peace be upon him.