Abdullah bin Abbas reported,
Ibn Abbas said, "Umar used to invite me to sit with the companions of Muhammad ﷺ, and he would tell me, 'Do not speak until they have spoken.'"He continued, "So he called them together and asked them about Laylat al-Qadr. He said, 'What do you make of the words of the Messenger of Allah ﷺ, "Seek it in the last ten nights"? Which night do you think it is?'Some of them said, 'The twenty-first night.' Others said, 'The twenty-third.' Another said, 'The twenty-fifth.' I stayed silent.Umar said, 'Why do you not speak?'I said, 'If you permit me, Commander of the Faithful, I will speak.'He said, 'I only sent for you so that you would speak.'I said, 'Shall I tell you my own view?'He said, 'That is exactly what we are asking you for.'I said, 'The seventh. I have observed that Allah 
mentioned seven heavens, and of the earth seven, and that He created man from seven, and that the earth's growth comes from seven.'Umar said, 'You have told me things I already know. But what about what I do not know? What do you mean by, "the earth's growth comes from seven"?'I said, 'Allah says, "Then We split the earth in fissures and caused to grow within it grain, and grapes and herbage, and olives and palm trees, and dense gardens, and fruit and pasture" [Abasa 80:26–31]. And abb is what the earth produces that livestock eat but people do not.'Then Umar said, 'Were you all unable to say what this young man has said, whose skull has not even knit together yet? By Allah, I hold no view but the one you have stated.' Then he said to me, 'I had ordered you not to speak until they had spoken. Now I order you to speak along with them.'"
Azami 4689
Hasanعن عبد الله بن عباس
قال كان عمر يدعوني مع أصحاب محمد ﷺ، فيقول لي: لا تكلم حتى يتكلموا. قال: فدعاهم، فسألهم عن ليلة القدر، فقال: أرأيتم قول رسول الله ﷺ: التمسوها العشر الأواخر. أي ليلة ترونها؟ فقال بعضهم: ليلة إحدى، وقال بعضهم: ليلة ثلاث، وقال آخر: خمس، وأنا ساكت. قال: فقال: ما لك لا تتكلم؟ قال: قلت: إن أذنت لي يا أمير المؤمنين تكلمت؟ قال: فقال: ما أرسلت إليك إلا لتتكلم. قال: فقلت: أحدثكم برأيي؟ قال: عن ذلك نسألك. قال: فقلت: السبع. رأيت الله عز وجل ذكر سبع سماوات، ومن الأرض سبعا، وخلق الإنسان من سبع، ونبت الأرض سبع. قال: فقال: هذا أخبرتني ما أعلم، أرأيت ما لا أعلم، ما هو قولك: نبت الأرض من سبع؟ قال: فقلت: إن الله يقول: {ثم شققنا الأرض شقا فأنبتنا فيها حبا وعنبا وقضبا وزيتونا ونخلا وحدائق غلبا وفكهة وأبا} [سورة عبس ٢٦-٣١]. والأب: نبت الأرض مما يأكله الدواب ولا يأكله الناس. قال: فقال عمر: أعجزتم أن تقولوا كما قال هذا الغلام الذي لم تجتمع شؤون رأسه بعد، إني والله ما أرى القول إلا كما قلت. وقال: قد كنت أمرتك أن لا تكلم حتى يتكلموا، وإني آمرك أن تتكلم معهم.
Imam Ahmad (85), Bazzar (210), and Abu Yaala (165) narrated it, and Ibn Khuzayma (2172) and Hakim (1/437-438) graded it sahih, all of them from the hadith of Asim bin Kulayb Jarmi, from his father, from Ibn Abbas, and he related it. The wording given here is Ibn Khuzayma's. Hakim said, "Sahih according to the criteria of Muslim." Its chain is hasan because of Asim bin Kulayb, for his hadith is hasan.Imam Ahmad also mentioned it in a shortened form, from Asim bin Kulayb, who said, "My father narrated it to me, and I related it to Ibn Abbas, who said, 'What amazes you about that?'" Umar, whenever he summoned the elders among the companions of Muhammad 
, would call me along with them, and he would say to me, "Do not speak until they have spoken." He said, "He called us one day, or one night, and said, 'The Messenger of Allah said about Laylat al-Qadr what you already know, "Seek it on an odd night in the last ten nights." So on which odd night do you think it is?'"Bayhaqi (4/313) also narrated it via the route of Abdul-Razzaq, who said, Maamar informed us, from Qatada and Asim, that both of them heard Ikrima say, Ibn Abbas said, Umar summoned the companions of the Prophet and asked them about Laylat al-Qadr, and they agreed that it was in the last ten nights. So I said to Umar, "I know, and I think I know which night it is." He said, "Which night is it?" I said, "The seventh that passes, or the seventh that remains, of the last ten nights." He said, "How do you know that?" I said, "Allah created seven heavens and seven earths and seven days, and time revolves in cycles of seven, and He created man, who eats and prostrates on seven limbs, and the tawaf is seven, and the pelting of the jamarat is seven." Umar said, "You have grasped something we did not grasp."Bayhaqi said in Fadail Awqat (p. 244), quoting his teacher Halimi, "All of this is inference, and not certainty. The Messenger of Allah knew it from the beginning, but he was not given permission to disclose it, lest people rely on knowing it and so devote themselves to worship only on that night while neglecting the rest of the nights..."On this subject there is also a narration from Ibn Masud, who said, a man came to the Prophet and asked, "When is Laylat al-Qadr?" He said, "Which of you remembers the night of the Sahbawat?" Abdullah said, "I would give my father and mother for you. I had some dates in my hand which I was eating for suhur, hidden behind the back of my saddle, and that was when Fajr broke."Imam Ahmad narrated it (3565, 3764), as did Abu Yaala (5393), Tabarani in Kabir (10/152), and Tahawi in his commentary (4548), all of them via the route of Masudi, from Saeed bin Amr, from Abu Ubayda, from Abdullah bin Masud, and he related it.This chain contains a discontinuity, for Abu Ubayda, who is the son of Abdullah bin Masud, did not hear from his father. Masudi is Abdul-Rahman bin Abdullah bin Utba, who became confused in memory toward the end of his life, but in some of the routes there are those who heard from him before this confusion set in, among them the teacher of Imam Ahmad, Amr bin Haytham Abu Qatan, who said, "Masudi narrated to us." So the defect is confined to the discontinuity in the chain.As for his saying "the night of the Sahbawat," they interpreted it as referring to the night of the twenty-seventh.