Abu Dawud said: All sound traditions from the Prophet (ﷺ) say: "He should make atonement for his oath," except those versions which are not reliable.
Abu Dawud said: I said to Ahmad: Yahya b. Sa'id (al-Qattan) has transmitted this tradition from Yahya b. 'Ubaid Allah. He (Ahmad b. Hanbal) said: But he gave it up after that, and he was competent for doing it. Ahmad said: His (Yahya b. 'Ubaid Allah's) tradition are munkar (rejected) and his father is not known.
In-book : Book 22, Hadith 33
English translation : Book 21, Hadith 3268