Assalam Alaykum wa Rahmatullah wa Barakatuhu,

I begin in the name of Allah and All thanks and praise belongs to Allah. I testify that there is none worthy of worship except Allah, and I testify that Muhammad SAW is His last and final messenger.

There are many hadith about surah Ya Sin and its benefits that have reached us. Although there is a scholarly debate about the authenticity of most of them, the experiences of the people indeed show that there is a great deal of benefit in reciting Surah Ya Sin.

Reciting Ya Sin as a way of magnifying the power of one's dua seeking Allah's pleasure and blessings, dispelling of difficulties such as blockages in one's spirituality, health, wealth, studies, marriage and children has been long known and practiced wazifa.

The sheer amount of stories from people who have witnessed the miracle of reciting Ya Sin is just overwhelming.

All that being said, it must be also said that this practice started as an experimentation of some pious people after life of Prophet SAW.

Some of my brothers and sisters fear that this might be a bidaa and after much learning, duas and istikhara, I have come to the conclusion that it is not an innovation and that Allah is pleased with the one who reads it. It is my ijtihad as well as the ijtihad of many righteous people of the past so you may accept it or leave it and we can still love each other for the sake of Allah.

Why is this not a bidaa?
Bidaa is anything that is brought into the deen which is not part of it. Quran is part of the deen and surah Yasin is part of the Quran.
Dua is part of the deen and making dua after reading Quran is an acceptable practice.
No one says it is obligatory for you to do this and no one says that it should be done at a certain fixed time or else bees will stop buzzing.

Why 41 times?
You can read it 1 time or 1000 times. Whatever you wish really, it is Quran and every letter of it is 10 good deeds for you.
You are actually done with the wazifa at 40, but we read 1 more to to honor the Quran and show that we are not done reading Ya Sin and we will continue to come back to it again and again. The same way when people do khatm of the Quran, they read Fatiha after it.

Okay.... then why 40?
Given the length of the Surah - reading it 40 times seems long enough that a person shows their dedication and desperation in seeking Allah's help and short enough that it can be done.
No one doubts the specialty of number 40 in Islam.
Prophet Muhammad received revelation at 40
Prophet Musa fasted 40 days before the special meeting with Allah in which he was given the Torah - the Inscribed Tablets.
The Quran mentions reaching the age of 40 and prescribes a dua for those who live that long. Look it up - Quran 46:15

Due to its occurrence in so many sacred texts, it is easy to conclude that there is some spiritual secret in the number 40. If you don't like it, then go for 70 or 313, more power to you :)

Does Surah's of the Quran really have these so called benefits??
Yes indeed! Some of them Prophet SAW actually told us. For example reading Surah Waqiah will increase your wealth, or reading Surah Kahf every Friday, you will find protection from Dajjal. Reading Ikhlas has the reward of third of the Quran and surah Mulk intercedes for its reciter. Daleel!!! Where is your PROOF PROFESSOR?! You can look them up yourself :) Ask your sheikh Google.

Some of them The Prophet SAW did not tell us and Allah made it known through other means such as reading Ayatul Kursi at night is protection from Shaitan or that Surah Al-Fatiha has healing in it.
The Quran is the words of Allah! How can you think it will not benefit?

Okay those surahs are fine but there is nothing about Ya Sin!!?
Simple logic. If those Surahs have these benefits, then so do all the others because they are all words of Allah and that is why the people of Allah went to seek out hidden treasures by way of experimentation. The term for this in the realm of Islamic Knowledge is "Mujarrabaat" for the seekers who would like to know.

Did they find anything?
Yes they did. And I'm sharing it with you.
You can try it for yourself and see.

Say: "In the bounty of Allah, and in His Mercy [Muhammad] - in that, let them rejoice": that is better than the (wealth) they hoard."

My final advice for people - Quran has indeed all these benefits, but they are secondary to the purpose of the Quran. There is nothing wrong seeking the blessing of the Quran, but do learn the message of it and apply it in your lives. May Allah bless you and grant you all goodness!