Ibn 'Abbas (رضي الله عنه) said:

Someone came to me in a dream during Ramadan, and it was said to me: Tonight is Lailatal-Qadr. So I got up, although I was drowsy, and I came to the Messenger of Allah (ﷺ) and found him praying. I looked to see what night that was, and it was the night of the twenty-third.