Sayyiduna Salman al-Farisi (may Allah be pleased with him) narrates that the Prophet (peace and blessings be upon him) said: Whoever recites: 'Allahumma inni ushhiduka, wa ushhidu mala'ikataka, wa hamalata 'arshika, wa ushhidu man fis-samawati annaka antallahu, la ilaha illa anta, wahdaka la sharika laka, wa ashhadu anna Muhammadan 'abduka wa rasuluka' (O Allah, I make You my witness, and I make Your angels and the bearers of Your Throne my witnesses, and I make whoever is in the heavens my witness, that You alone are Allah; there is no deity except You; You alone are the deity, You have no partner; and I testify that Sayyiduna Muhammad (peace and blessings be upon him) is Your servant and Your Messenger),
(the Prophet, peace and blessings be upon him, says:) whoever recites these words once, Allah Almighty frees one third of him from Hell; whoever recites these words twice, two thirds of him are freed from Hell; and whoever recites these words three times, his whole being is freed from Hell.
Bazzar recorded it from his teacher Ahmad, without giving his lineage; its chain contains a narrator, Humayd, the freed slave of Abu Alqamah, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الأذكار / 16828