Eternal sin
Thomas Aquinas lists, or has responded to, six sins that supposedly go against the Holy Spirit:
Thomas Aquinas explains that the unforgivability of blasphemy against the Holy Spirit means that it removes the entrance to these means of salvation; however, it cannot hinder God in taking away this obstacle by way of a miracle.
God in Islam
Tawhid constitutes the foremost article of the Muslim profession. The deification or worship of anyone or anything other than God (shirk) is the biggest sin in Islam. The entirety of the Islamic teaching rests on the principle of Tawhid.