Musannaf Ibn Abi Shayba 28:873

Rayhan ibn Sa'id narrated to us, he said: Marzuq ibn 'Amr narrated to me, he said: Abu Farqad narrated to me, he said: We were with Abu Musa al-Ash'ari on the day we conquered the market of al-Ahwaz. A man from the polytheists ran, and two men from the Muslims ran after him. While he was running and they were running, one of them said to him, "Matras." So he took him, and they brought him while Abu Musa was striking the necks of the captives, until the matter reached this man. One of them said, "Indeed, security has been granted to this one." Abu Musa said, "And how was security granted to him?" He said, "He was running away on the land, so I said to him, 'Matras,' and he stopped." Abu Musa said, "And what is 'Matras'?" He said, "Do not fear." He said, "This is security; let him go." So they let the man go.