The Prophet ﷺ said regarding Laylat al-Qadr, "Laylat al-Qadr is the night of the twenty-seventh."
عن النبي ﷺ في ليلة القدر، قال: ليلة القدر، ليلة سبع وعشرين.
Abu Dawud (1386) narrated it from Ubaydullah bin Muaz, who said, my father narrated to us, Shubah informed us, from Qatada, that he heard Mutarrif, from Muawiya bin Abu Sufyan, and he mentioned it.Bayhaqi (4/302) reported it through the route of Abu Dawud, and Ibn Hibban graded it sahih (3680). Its chain of transmission is sahih.