Musnad Ahmad 928:20

Abdullah narrated to us, Abbas ibn al-Walid al-Narsi narrated to me, he said: Hammad ibn Shu’ayb narrated to us, from ‘Asim, from Zirr ibn Hubaysh, from Abdullah: That he said regarding the Night of Decree (Laylat al-Qadr): "Whoever stands [in prayer] throughout the year will encounter it." So I departed until I arrived at Uthman ibn Affan, and I intended to meet the companions of the Messenger of Allah (peace and blessings of Allah be upon him) from the Muhajirun and the Ansar. ‘Asim said: He narrated to me that he kept company with Ubayy ibn Ka’b and Abd al-Rahman ibn Awf, and he claimed that they used to stand [in prayer] when the sun set, and they would perform two rak’ahs before the Maghrib prayer. He said: So I said to Ubayy—and there was some harshness in him—: "Lower your wing for us, may Allah have mercy on you, for I am only benefiting from you." He said: "Do you want to not leave a single verse in the Quran without asking me about it?" He said: And I had a sincere companion, so I said: "O Abu al-Mundhir, inform me about the Night of Decree, for Ibn Mas’ud says: 'Whoever stands throughout the year will encounter it.'" He said: "By Allah, Abdullah knew that it is in Ramadan, but he wanted to keep it obscure for the people so that they would not rely [solely on that]. By the One who sent down the Book upon Muhammad, it is indeed in Ramadan, and it is the night of the twenty-seventh." I said: "O Abu al-Mundhir, how did you know that?" He said: "By the sign that Muhammad (peace and blessings of Allah be upon him) informed us of." We counted and memorized, and by Allah, it is indeed as he described, without exception. I said: "And what is the sign?" He said: "It rises when it rises, having no rays, until it ascends." And ‘Asim was, on that night, from the time of the pre-dawn meal, not eating any food, until when he prayed the Fajr, he climbed the minaret and looked at the sun when it rose, having no rays, until it turned white and ascended.