Abu Dawud Book 2, Hadith Number 1002.
Narated By Al-Azraq ibn Qays : An imam of ours, whose kunyah (surname) was AbuRimthah, led us in prayer and said: I prayed this prayer, or one like it, with the Prophet (PBUH). AbuBakr and Umar were standing in the front row on his right and there was a man who had been present at the first takbir in the prayer. The Prophet of Allah (PBUH) offered the prayer, then gave the salutation to his right and his left so that we saw the whiteness of his cheeks, then turned away as AbuRimthah (meaning himself) had done.
The man who has been present with him at the first takbir in the prayer then got up to pray another prayer, whereupon Umar leaped up and, seizing him by the shoulders, shook him and said: Sit down, for the People of the Book perished for no other reason than that there was no interval between their prayers.
The Prophet (PBUH) raised his eyes and said: Allah has made you say what is right, son of al-Khattab.