What is the ruling on a man who unintentionally blasphemed Allaah? Is this disbelief?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

According to the consensus of the Muslim scholars blaspheming Allaah The Almighty is an act of disbelief that takes a person out of the fold of Islam. However, if a person blasphemes Allaah out of the slip of the tongue, then he is not sinful, as Allaah Says (what means): {And there is no blame upon you for that in which you have erred but [only for] what your hearts intended. And ever is Allaah Forgiving and Merciful.}[Quran 33:5]

Ibn ‘Abbaas said regarding the Saying of Allaah (which means): {Whether you show what is within yourselves or conceal it, Allaah will bring you to account for it}[Quran 2:284] When this verse was revealed, the companions felt sad because they thought they would be held accountable for the thoughts and ideas they could not avoid. So, the Prophet, sallallaahu ‘alayhi wa sallam, ordered them to say: "We have heard, obeyed and submitted." Having obeyed the instructions of the Prophet, sallallaahu ‘alayhi wa sallam, Allaah put faith in their hearts and revealed the verse (which means): {Allaah does not charge a soul except [with that within] its capacity. It will have [the consequence of] what [good] it has gained, and it will bear [the consequence of] what [evil] it has earned. "Our Lord, do not impose blame upon us if we have forgotten or erred. Our Lord,} Allaah Said: "I Did" {Our Lord, and lay not upon us a burden like that which You laid upon those before us.} Allaah Said: "I Did" {And pardon us; and forgive us; and have mercy upon us. You are our protector,}[Quran 2:286] Allaah Said: "I Did". [Muslim]

Thus, if the blaspheming happened unintentionally and out of the slip of the tongue, as stated by the questioner, then the person is not sinful.  

Allaah Knows best.