According to the scholars, verbally articulating the intention for prayer is neither required nor recommended; on the contrary, it is considered to be an innovation that violates Islamic law. Many scholars, at different times and in different countries, have verified that it is an act of innovation in religion, so anyone who says that it is from the sunnah is totally mistaken. If someone declares the intention out loud because he thinks it is legal, then he or she is astray and uninformed and deserving of punishment. If the person insists on articulating the intention after it has been made clear to him or her that it is illegal, then he or she should be punished, especially when causing harm to those beside him or her in prayer by stating the intention loudly and frequently.
Aa’isha said: “The prophet used to start the prayer with takbeer” (1)
Abu Hurayrah said that the messenger of Allah entered the masjid, and a person also entered therein and offered prayer, and then came and greeted the messenger of Allah. The messenger of Allah returned his greeting and said: “Go back and pray, for you have not offered the prayer.” He prayed again as he had prayed before, then came to the messenger of Allah and greeted him. The messenger of Allah returned the greeting and said: “Go back and perform the prayer, for you have not offered the prayer.” This (act of repeating the prayer) was done three times. Upon this, the person said: “By Him who has sent you with the truth, i do not know any better than this, please teach me.” He said: “When you get up to pray, recite takbeer, and then recite whatever you conveniently can from the Qur’an. Then bow until you are at rest while bowing, then rise up until you have stood up completely, then prostrate until you are at rest while prostrating, then rises up until you are at rest sitting. Do that in all of your salaah.”(2)
Abdullah ibn Umar narrated: I saw Allah’s messenger opening the prayer with the takbeer and raising his hands to the level of his shoulders at the time of saying the takbeer. (3)
These hadiths, and many others which describe the acts of our Prophet sallallahu alayhi wa sallam, shows that the prayer is opened by pronouncing the takbeer only, with nothing before it. This point is confirmed by unanimous agreement of the scholars that if what is spoken with the tongue contradicts what is in the heart, the accountability is reckoned by what is in the heart. In that case, what is the use of the spoken intention?
Taken from Common Mistakes regarding Prayer of Shaykh Mashhur Hasan Salman