Musnad Ahmad 656:1

Abu Dawud narrated to us, Hisham narrated to us, from Qatadah, from Khallas, from Abdullah ibn Utbah, who said: Ibn Mas’ud was approached regarding a man who married a woman, then died leaving her, without having specified a dowry for her, and without having consummated the marriage with her. He was asked about her for a month, but he did not say anything regarding it. Then they asked him, and he said: "I will speak regarding her according to my opinion. If it is an error, then it is from me and from Satan, and if it is correct, then it is from Allah: She has the dowry of one of her peers, she has the inheritance, and she must observe the waiting period (iddah)." A man from Ashja’ stood up and said: "I bear witness that you have judged regarding it with the judgment of the Messenger of Allah (peace and blessings of Allah be upon him) in the case of Birwa’ bint Washiq." He (Ibn Mas’ud) said: "Bring your two witnesses." So Al-Jarrah and Abu Sinan, two men from Ashja’, testified for him.