Sayyiduna Abu Sa‘id Khudri (may Allah be pleased with him) narrates: A man heard another man reciting Surah Al-Ikhlas repeatedly. The next day, he came to the Prophet Muhammad (peace and blessings be upon him) and mentioned this to him, considering that person to regard this Surah as insignificant. The Prophet Muhammad (peace and blessings be upon him) said to that person, “By Him in Whose Hand is my soul, it is equal to one third of the Qur’an.”
Hadith Referenceصحیح ابن حبان / كتاب الرقائق / 791
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - «صحيح أبي داود» (1314): خ.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط الشيخين.