Mustadrak al-Hakim — Hadith 6430

It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that whenever Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) invited the senior Companions of the Messenger of Allah (peace and blessings be upon him), he would call me along with them. One day, or one night, he called us and said: "You know what the Messenger of Allah (peace and blessings be upon him) said about Laylat al-Qadr: 'Seek it in the last ten nights.' So which of the odd nights do you think it may be?" Some said: the ninth night; some said the seventh, someone the fifth, and someone the third. Then he asked me: "O Ibn Abbas! Why do you not speak?" I said: "If you permit me, I will speak." He said: "I called you only so that you would speak." I asked: "Shall I give my own opinion?" He said: "It is your opinion that I am asking you for." So I said: "I have seen that Allah Almighty has given great importance to the number seven: He made the heavens seven and the earths seven, and (in mentioning the vegetation of the earth) He said: 'Then We split the earth, splitting it (26) and caused to grow in it grain (27) and grapes and herbage (28) and olives and date palms (29) and gardens of dense trees (30) and fruit and fodder' [Surah Abasa: 26 - 31]. By 'hada'iq' (gardens) is meant every tree that intertwines with others until it becomes a garden, and by 'abb' is meant the vegetation that grows from the earth which people do not eat (but which is fodder)." Then Sayyiduna Umar (may Allah be pleased with him) said (to the other Companions): "Were you unable to say something like what this young man has said, the sutures of whose skull have not yet fully joined?" Then he said to me: "I had (previously) forbidden you to speak, but now whenever I invite you along with them, you must speak."
This hadith has a sahih (authentic) chain of narration, but the two Shaykhs (Bukhari and Muslim) did not record it.