Sayyiduna Anas bin Malik (may Allah be pleased with him) states: The Prophet (peace and blessings be upon him) saw a man moving the pebbles while he was praying. When he had finished the prayer, the Prophet (peace and blessings be upon him) said to that man: This is your share of the prayer.
Abu Ya'la and Bazzar recorded it; its chain contains Yusuf bin Khalid al-Samti, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2475