Is it permissible to send peace or blessings upon al-Mahdi? My Quran teacher did something among those lines during our congregational dua' and on another occasion she wanted us to recite the fatiha for a deceased person, which i forgot was not from the sunna at that moment, am i sinful? Also should i continue studying with her? Since she did help me to improve my reading of the Quran.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

There is nothing in the Sharee’ah about what was reported in regard to sending blessings upon the Mahdi. Sending blessings upon the Mahdi is one of the practices of innovators. Therefore, it is not permissible for a Muslim to participate with them in it, and it is not mentioned in the Sharee’ah to recite Al-Fatihah on the soul of the dead.

Reciting the Quran and dedicating its reward to the dead, even if it lawful according to a group of scholars, but specifying a particular Soorah (Chapter) and making this a habit, renders the matter not permissible and makes it an innovation, because it is a specification of what the Sharee’ah did not specify.

Indeed, many innovations start at the beginning like this and then become a followed Sunnah, and the one who denies it is rebuked and condemned.

Moreover, many of those who recite Al-Fatihah on the dead do not do so while intending gifting its reward, but they do it by imitating others.

Hence, if that teacher belongs to one of the innovated sects, then you should not let her teach you as she may drag you into her innovation and familiarize you with some conceptions by which you will be affected, while you don’t have enough knowledge to repel them.

Therefore, you should fear Allah and seek knowledge with knowledgeable people.

Muslim reported from Muhammad ibn Sireen, who said: “Indeed this knowledge is religion, so carefully consider from whom you take your religion.”

The same thing was reported from Ismail ibn Abu Uways who said: “I heard my uncle Maalik saying: ‘Indeed this knowledge is religion, so carefully consider from whom you take your religion.’” [End of quote]

As for your saying “I forgot ... Am I sinful”; then the answer is that we hope that there is no sin on you.

Forgetfulness exempts one from being sinful. Allah Says (what means): {"Our Lord, do not impose blame upon us if we have forgotten or erred. Our Lord, and lay not upon us a burden like that which You laid upon those before us. Our Lord, and burden us not with that which we have no ability to bear."} [Quran 2:286]

In response to this, Allah said: “Indeed, I have done so.”, as in Saheeh Muslim.

Another Hadeeth reads: “Allah has forgiven my Ummah (nation) for mistakes, forgetfulness and that which they are forced to do.” [Ibn Majah, Ibn Hibban and others]

The meaning of the Hadeeth – as stated by the scholars – is that Allah has forgiven this nation sin and excepted them from hardship for thing which they do by mistake, forgetfulness, or coercion.

Allah knows best.