Deduction from “Lailatul Qadr”
In Surah Qadr, the words, “Lailatul Qadr” have been mentioned thrice. There are 9 letters in Arabic in the said word and that 9 when multiplied by 3 is 27. Thus, this number also suggests that Shab Qadr is on the 27th night, as ‘Allama Hafidh Ibn Hajar ‘Asqalani (May Allah shower His mercy on him) has written:
Translation: And some scholars have deduced (that Shab Qadr is on the 27th) in yet another way. Thus, it is related that Lailatul Qadr has 9 letters (in Arabic script) and in this Surah (i.e. Surah Qadr), it has been mentioned thrice. This way, it comes to 27. (Fath Ul Bari; Mafateeh Ul Ghaib, Surah Qadr-03)