Abdullah bin Abbas reported,
What may surprise you about that is this. Whenever Umar 
would summon the senior companions of Muhammad ﷺ, he would summon me along with them. He would say to me, "Do not speak until they have spoken."One day, or one night, he summoned us and said, "The Messenger of Allah ﷺ has said about Laylat al-Qadr what you already know, that you should seek it in the last ten nights on an odd-numbered night. So which of the odd nights do you think it falls on?"
Ahmad 85
Sahihحدثنا عفان حدثنا عبد الواحد بن زياد قال حدثنا عاصم بن كليب قال قال أبي فحدثنا به
ابن عباس رضي الله عنهما قال
وما أعجبك من ذلك كان عمر رضي الله عنه إذا دعا الأشياخ من أصحاب محمد ﷺ دعاني معهم فقال لا تتكلم حتى يتكلموا قال فدعانا ذات يوم أو ذات ليلة فقال إن رسول الله ﷺ قال في ليلة القدر ما قد علمتم فالتمسوها في العشر الأواخر وترا ففي أي الوتر ترونها
Its isnad is sahih. Asim bin Kulayb is trustworthy. His father, Kulayb bin Shihab bin Majnun Jarmi, is a trustworthy follower of the companions. Some have mistakenly listed him among the companions themselves, see Isabah 5:331.As for Asim's statement, "My father said, so we told it to Ibn Abbas," it contains an abridgement. It appears that a prior conversation had taken place among them concerning Laylat al-Qadr, in which Kulayb related something to them. Then he said to them, "So we told it to Ibn Abbas," meaning that he informed Ibn Abbas of what he had heard, and Ibn Abbas said to him, "What is it about that which amazes you," and so on.See also Sunan al-Kubra of Baihaqi, 4:308-309. The hadith will come again in abridged form at 2981.