The Messenger of Allah ﷺ was asked about Laylat al-Qadr, and he said, "It is in the last ten nights, either on the fifth or on the third."
أن رسول الله ﷺ سئل عن ليلة القدر، فقال: هي في العشر الأواخر، أو في الخامسة، أو في الثالثة.
It was narrated by Ahmad in Musnad (22043), and Tabarani in Al-Kabir (20/92) from the hadith of Baqiya bin Walid, who said, "Buhayr bin Saad narrated to me, from Khalid bin Madan, from Abu Bahriya, from Muaz bin Jabal," who said, and then he mentioned it. Its isnad is hasan because of Baqiya bin Walid, for he is truthful when he states his source explicitly, but otherwise he engages heavily in concealing weak narrators in his chains. He did state his source explicitly in Ahmad's narration. Some scholars of knowledge have stipulated that this explicit statement must occur at every level of the chain, while the majority hold that it is accepted if he states his source explicitly at the level of his own teachers. Abu Bahriya's name is Abdullah bin Qays al-Kindi al-Himsi, a trustworthy narrator, and he is well known by his kunya.On this subject there is also what was narrated from Ibn Abbas, that the Prophet ﷺ came to them hurriedly. He said, "Until he alarmed us with his haste. When he reached us, he said, 'I came in haste to tell you about Laylat al-Qadr, but it was made me to forget it, between me and you. But seek it in the last ten nights of Ramadan.'" It was narrated by Imam Ahmad (2352) and Tabarani in Al-Kabir (12621), both through the route of Qabus bin Abu Dhubyan, from his father, from Ibn Abbas, and then he mentioned it. Qabus is disputed, and most scholars of knowledge hold that he is daif, to the point that Ibn Hibban said, "He transmits alone from his father things that have no basis." I say, it is not as he said, for this hadith has many corroborating narrations as has already been shown, except for his statement, "It was made me to forget it, between me and you." As for Abu Dhubyan, he is Husayn bin Jundab al-Janbi al-Kufi, one of the narrators accepted by the community of scholars.