Shaykh Saalih Al-Fawzaan (hafidahullah) was asked:
In our country, we know that every act of worship must have an intention for it. Due to this, then it’s a must to pronounce the intention before commencing the prayer (or any other act of worship). So, if this is not allowed, or is an innovation, then what is the meaning of the hadeeth: “Verily actions are by intentions…”?
The Shaykh answered:
Yes. Every action requires an intention, due to the hadeeth that you mentioned; that the Messenger (sallallaahu alaihi wa sallam) said
“Verily actions are by intentions, and for every person is what he intended.” (1)
However the meaning (of this) is not to pronounce the intention verbally. The meaning is that you believe and intend with your heart, the performance of worship sincerely for Allah (azza wa jal)- and suffice with this.
Therefore the place of intention is the heart and not the tongue. Pronouncing the intention is an innovation, because it is not (authentically) established from the Prophet (sallallaahu alaihi wa sallam); or from his Rightly-Guided Caliphs; or his Companions; or the Virtuous Generations.
It is not established that they would pronounce the intention, for indeed the place of intention is only the heart. Allah says:
قُلۡ أَتُعَلِّمُونَ ٱللَّهَ بِدِينِڪُمۡ وَٱللَّهُ يَعۡلَمُ مَا فِى ٱلسَّمَـٰوَٲتِ وَمَا فِى ٱلۡأَرۡضِۚ وَٱللَّهُ بِكُلِّ شَىۡءٍ عَلِيمٌ۬ (الحُجرَات:16)
Say: “Will you inform Allâh of your religion While Allâh knows all that is in the heavens and all that is in the earth, and Allâh is All-Aware of everything”. (Al-Hujuraat: 16)
So, if you intend with your heart, then Allah knows; and he does not need that you pronounce (your intention) with your tongue.
Slightly paraphrased from Majmoo’ Fataawa of Shaykh Saalih Al-Fawzaan (hafidahullah) Vol. 2 Page 675
(1) Al-Bukhaari Hadith Nos: 1, Muslilm: 1907