Sayyiduna Abdullah bin Amr (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "Whoever recites Surah al-Ikhlas has recited one third of the Qur'an."
Al-Tabarani recorded it in al-Mu'jam al-Kabir; its narrators are thiqat (trustworthy). (Allamah al-Haythami says:) I say: Many hadiths about this will come in the chapter on the tafsir of Surah al-Ikhlas, if Allah wills.