Musannaf Ibn Abi Shayba 3:5466

Ghundar narrated to us, from Shu'bah, who said: I asked Hammad about the pebbles that one takes out of the mosque. He said: "Throw them away." And I asked al-Hakam, and he said: "Tie them up until you return them, for it has reached me that they have a cry."