It is narrated from Sayyiduna Anas bin Malik (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever recites 'Qul huwa Allahu ahad' (Surah al-Ikhlas), it is as though he has recited one third of the Qur'an."
The author of the book said: "This hadith is narrated from Burayd bin Abi Maryam (may Allah have mercy on him) only with this chain, and Zayd bin Akhzam (may Allah have mercy on him) is alone in narrating it."
It is like this in the Dar al-Haramayn edition, and the correct name is probably Muhammad bin Abbad al-Huna'i, as in Musnad al-Bazzar; and Allah knows best.
Hadith Referenceالمعجم الأوسط / باب الميم / 7336
Hadith Takhrij«أخرجه الضياء المقدسي فى «الأحاديث المختارة» برقم: 1698، 2464، 2465، 2466، والترمذي فى «جامعه» برقم: 2893، وابن ماجه فى «سننه» برقم: 3788، وأبو يعلى فى «مسنده» برقم: 1481، 4118، 4136، والبزار فى «مسنده» برقم: 6469، 7006، 7581، والطحاوي فى «شرح مشكل الآثار» برقم: 1213، والطبراني فى «الأوسط» برقم: 2035، 5730، 7287»