Assalamu Alaikum! I've heard that many says that it's good to cut off the baby's hair for 40 Wednesdays continuously.By doing this they says baby will have good knowledge. Is there such thing according to Islam? I want to know if there any references regarding this is to be founded in Hadees or Qur'an?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

We do not know of any Islamic text supporting what you mentioned in the question. According to the Islamic Sharee'ah, it is prescribed to shave the baby’s hair on the seventh day of birth, whether it is a Wednesday or not. This is evidenced by what Samurah ibn Jundub reported, that the Prophet, sallallaahu ‘alayhi wa sallam, said: “Every boy is a security for his ‘Aqeeqah, to be slaughtered for him on the seventh day of his birth, and his head is to be shaved and he is to be given a name.” [Ahmad and An-Nasaa’i]

‘Ali ibn Abi Taalib said: “The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, offered the ‘Aqeeqah for Al-Hasan as one sheep, and said: ‘O Faatimah! Shave his head and give the weight of his hair in silver as charity.’ So she weighed it, and it was the weight of a Dirham or part of a Dirham.” [At-Tirmithi, Al-Haakim, and others - Al-Albaani graded it Saheeh (sound)]

As for the claim that shaving the baby’s head every Wednesday for 40 weeks to make him have good knowledge, then, as far as we know, there is no revealed evidence for this. Whoever argues that this is prescribed in Islam is required to produce evidence supporting his claim.

For further benefit, please refer to Fataawa 81275 and 90729.

Allaah Knows best.