Musannaf Ibn Abi Shayba 18:1120

Abu Bakr narrated to us, he said: Abd al-Rahim narrated to us, from Ash'ath, from Ibn Sirin, from Shurayh: He said: A Qasamah (oath-taking) came, and they did not complete fifty [oaths]. So he returned the Qasamah to them until they completed them.