Musnad Ahmad 830:90

'Affan narrated to us, Hammad bin Salamah narrated to us, Thabit informed us, that Abu Bakrah said: "The Messenger of Allah (ﷺ) forbade *al-khadhf* (flicking pebbles with the fingers)." A cousin of his then took [a pebble] and flicked it. [Abu Bakrah] said: "Do you do this? I inform you that the Messenger of Allah (ﷺ) forbade it, and you are flicking [pebbles]! By Allah, I will not speak to you in Arabic as long as I live," or "as long as I remain," or something similar to this.