Urwah bin al-Zubayr (may Allah have mercy on him) narrates from Sayyidah Aishah (may Allah be pleased with her) that she used to interpret this (verse) as follows: it is something a person swears upon, intending nothing but the truth by it, yet it turns out contrary to it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19942