Al-Burhan, Ibn Muflih (r) said:
❝The most likely night (to be Laylatu-l Qadr) is the 27th. Imam Ahmad (r) explicitly stated so, and it is the opinion of Ubay b. Ka’b (r) who used to swear by Allah that it was on this night.❞
Ubay b. Ka’b (r) said:
❝By Allah Ibn Mas’ud knew that it is in Ramadan and that it is on the 27th night, but he did not want to tell you so that you don’t become lax.❞
Graded Sahih by al-Tirmidhi.
Ibn ‘Abbas (r) would say:
❝Surah al-Qadr consists of 30 words, the 27th of which is هي [i.e. – “it (the night) is…”].❞