As mentioned by ad-Daarimee in his Sunan (1/79):
‘Amr ibn Salmah said: We used to sit by the door of ‘Abdullah ibn Mas’ood before the Morning Prayer, so that when he came out we would walk with him to the mosque. (One day) Abu Moosaa al-Ash’aree came to us and said: “Has Abu ‘Abd ar-Rahmaan come out yet?” We replied, “No”. So he sat down with us until he came out.
When he came out we all stood along with him, so Abu Moosaa said to him, “O Abu ‘Abd ar-Rahmaan! I have just seen something in the mosque which I deemed to be evil, but all praise is for Allaah, I did not see anything except good.” He enquired, “Then what is it?” (Abu Moosaa) replied, “If you live you will see it. I saw in the mosque people sitting in circles awaiting the Prayer. In each circle they had pebbles in their hands a man would say ‘repeat Allahu Akbar a hundred times.’ So they would repeat it a hundred times. Then he would say, ‘say Laa ilaaaha illallaah a hundred times’. So they would say it a hundred times. Then he would say, ‘say Subhaanallaah a hundred times.’ So they would say it a hundred times.”
(Ibn Mas’ood) asked, “What did you say to them?” (Abu Moosaa) said, “I did not say anything to them. Instead I waited to hear your view or what you declared.” (Ibn Masood) replied, “Would that you had ordered them to count up the evil deeds they acquired and assured them that their good deeds would not be lost!”
Then we went along with him (Ibn Mas’ood) until he came to one of these circles and stood and said, “What is this which I see you doing?” They replied, “O Abu ‘Abd ar-Rahmaan! These are pebbles upon which we are counting takbeer, tahleel and tasbeeh.” He said, “Count up your evil deeds. I assure you that none of your good deeds will be lost. Woe to you, O Ummah of Muhammad (صلى الله عليه وسلم)! How quickly you go to destruction! These are his (صلى الله عليه وسلم) clothes which have not yet decayed and his bowl which is unbroken. By Him in Whose Hand is my soul! Either you are upon a Religion better guided than the Religion of Muhammad (صلى الله عليه وسلم) or that you are opening the door of misguidance.”
They said, “O Abu ‘Abd ar-Rahmaan! By Allaah, we only intended good.” He said, “How many there are who intend good but do not achieve it. Indeed Allaah’s Messenger (صلى الله عليه وسلم) said to us ‘A people will recite the Qur’aan but it will not pass beyond their throats.’ By Allaah! I do not know, perhaps most of them are from you.” Then he left them.
Umar ibn Salmah (the sub-narrator) said: “We saw most of those people fighting against us on the day of Nahrawaan, along with the Khawaarij.”