This is forbidden on three counts:
1. The cause of self-praise is mostly pride and arrogance. So, in reality, what is forbidden is pride and arrogance.
2. As to the end of man, only Allah knows if it will come in a state of taqwa and taharah, that is, in a state when one is still God-fearing spiritually and free from major and minor impurities physically. Therefore, claiming sanctity for oneself is contrary to being God-fearing.
As such, Zaynab radhiAllahu anha daughter of Abi Salamah radhiAllahu anhu narrates that the Prophet sallAllahu aalyhi wa sallam asked her: “What is your name?” Since, at that time, her name was Barrah which means pure from sin, so, that was what she told him. He, then said,
“Do not claim sanctity for yourselves (i.e. do not claim purity and freedom from sins) because it is Allah alone who knows best as to who among you is of the righteous.”
He, then, named her Zaynab (instead of Barrah). [Mazhari]
3. The third reason for this prohibition is that such a claim gives people the false idea that the person making that claim is nearer to Allah because he is free of all faults, although this is a lie, for no mortal man is free of one or the other shortcoming. [Bayan-ul-Qur’an]
If impediments mentioned above do not exist, one can speak about one’s trait of character as an expression of gratitude for Allah’s blessing. [Bayan-ul-Qur’an]