Riyad as-Salihin, Book 9, Hadith 1194 (In-Book) ⓘ
'Aishah (May Allah be pleased with her) reported: The Messenger of Allah used to strive more in worship during Ramadan than he strove in any other time of the year; and he would devote himself more (in the worship of Allah) in the last ten nights of Ramadan than he strove in earlier part of the month.[Muslim].
وعنها قالت: كان رسول الله صلى الله عليه وسلم ، يجتهد في رمضان ما لا يجتهد في غيره، وفي العشر الأواخر منه، ما لا يجتهد في غيره" ((رواه مسلم)).