It is reported from Sayyiduna Ubayy bin Ka'b (may Allah be pleased with him), or perhaps from a man of the Ansar: The Prophet (peace and blessings be upon him) said: "Whoever recites Surah al-Ikhlas, it is as though he has recited one third of the Qur'an."
Ahmad recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب التفسير / 11547
Hadith Gradingمحدثین:إسنادہ صحیح
Hadith Takhrij«اخرجه احمد فى المسند (141/5) ، أخرجه مسند أحمد برقم: 20768»