Is the oath broken if one speaks to the intended person without recognizing them?

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If the oath taken was an oath of divorce (talaq) or manumission ('itq), the oath is broken. Imam Ahmad ruled that if a man swore by divorce not to speak to his mother-in-law, and he saw her at night and asked 'Who is this?', he has broken his oath because he spoke to her. However, if the oath was by Allah (billahi ta'ala) or an expiable oath, the correct view is that the oath is not broken, as the speaker did not intend to speak to the specified person, resembling forgetfulness or a meaningless utterance (laghw al-yamin), based on the understanding that he believed the person was someone else.