Ibn ʿAbbās reported that the Prophet (ﷺ) ﷺ said:

“Qul huwa Allāhu aḥad (Sūrat al-Ikhlāṣ) is equivalent to one-third of the Qur'ān, and Qul yā ayyuhal kāfirūn (Sūrat al-Kāfirūn) is equivalent to one-fourth of the Qur'ān.” Reference: Al-Silsilah al-Ṣaḥīḥah 586.

قال رسول الله صلى الله عليه وسلم: (قل يا أيها الكافرون تعدل ربع القرآن).