The Prophet ﷺ said, "Seek out Laylat al-Qadr in the last ten nights of Ramadan."
حدثنا ابن نمير حدثنا هشام عن أبيه
قال النبي ﷺ تحروا ليلة القدر في العشر الأواخر من رمضان
Its isnad is sahih. Bukhari narrated it 4/259 no. 2017 in Fath, and Muslim 2/228 no. 1169, both in the Book of Fasting, and the hadith has already appeared with the wording "Seek it..." See 11386, 15991, and 20705.