Amirul Momineen Hazrat Ali (a.s) Said:

"The Holy Prophet’s graces and virtues are so many in this world and Hereafter that they cannot be described fully. Yet I tell you that which you can digest and which your intelligence cannot deny. Doubtlessly, the graces of the Holy Prophet are so many that people of Hell say in regret: Why did we not respond to his call in our worldly lives?Describing their condition, the Holy Qur’an says:

“On the Day when their faces shall be turned into the fire they shall say: O would that we had obeyed Allah and obeyed the Apostle.”

Reference: Hayat Al Qulub, vol 2, section 9