Pronouncing the intention is a newly-invented practice (in religion) which neither the Prophet (peace be upon him) nor his Companions (may Allah be pleased with them) did. Therefore, it is not permissible to pronounce it, for the Prophet (peace be upon him) said:
Anyone who introduces anything into this matter of ours (Islam) that is not part of it will have it rejected.
According to another narration:
Anyone who does an action which is not in accordance with this matter of ours (Islam) will have it rejected.
Indeed, the intention is to be held in the heart.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.