6. Prayer (Kitab Al-Salat) Detailed Injunctions about Ramadan - كتاب شهر رمضان
4) Chapter: Whoever Said It Was The Seventeenth Night
Narrated Abdullah ibn Mas'ud:
The Messenger of Allah (ﷺ) said to us: Seek it (laylat al-Qadr) on the seventeenth night of Ramadan, and on the twenty first night, and on the twenty-third night. He then kept silence.