Musnad Ahmad 26:891

I read to my father from here, and he affirmed it, and he said: Muhammad ibn Idris al-Shafi‘i narrated to me, Sa‘id ibn Salim—meaning al-Qaddah—informed us, Ibn Jurayj informed us, that Isma‘il ibn Umayyah informed him, from ‘Abd al-Malik ibn ‘Umayr, that he said: I was present with Abu ‘Ubaydah ibn ‘Abd Allah ibn Mas‘ud, and two men came to him who had traded an item. One said: "I took it for such and such," and the other said: "I sold it for such and such." Abu ‘Ubaydah said: "‘Abd Allah ibn Mas‘ud was approached regarding the likes of this, and he said: 'I was present with the Messenger of Allah (may Allah bless him and grant him peace) when he was approached regarding the likes of this, and he ordered that the seller be made to swear an oath, then the buyer is given the choice: if he wishes, he takes it, and if he wishes, he leaves it.'" I read to my father, he said: I was informed by Hisham ibn Yusuf, regarding the two traders in the hadith of Ibn Jurayj, from Isma‘il ibn Umayyah, from ‘Abd al-Malik ibn ‘Ubayd. And he said: My father said: Hajjaj al-A‘war [said] ‘Abd al-Malik ibn ‘Ubayd.