Musannaf Ibn Abi Shayba 13:791

Abu Bakr narrated to us, he said: Isma'il bin 'Ayyash narrated to us, from 'Abd al-'Aziz bin 'Ubayd Allah, from al-Sha'bi, from Shurayh: That he used to permit a man's acknowledgment of a debt at the time of his death to a non-heir, and he would not permit it for an heir except with evidence.