Shaykh Muḥammad ibn Ṣāliḥ al-ʿUthaymīn (رحمه الله) said:1
Indeed, many of the general folk think that Laylah al-Qadr [i.e.the Night of Decree] is on the fifteenth of Shaʿbān, and what will occur in the upcoming year is written in it; however, it is known that Laylah al-Qadr is in Ramaḍān. The proof for that is His statement:
إِنَّا أَنزَلْنَاهُ فِي لَيْلَةِ الْقَدْرِ ﴿١﴾
‘Verily, We have sent it [this Qurʾān] down in the night of al-Qadr [Decree],’
And His statement:
حم ﴿١﴾ وَالْكِتَابِ الْمُبِينِ ﴿٢﴾ إِنَّا أَنزَلْنَاهُ فِي لَيْلَةٍ مُّبَارَكَةٍ ۚ إِنَّا كُنَّا مُنذِرِينَ ﴿٣﴾...