As much as the making of a niyah or intention is an obligatory act of prayer, there is absolutely no evidence in the authentic and established Sunnah of the Messenger of Allah (peace be upon him) that the Prophet (peace be upon him) verbally declared his intention to offer a particular prayer.

The intention one makes in ones heart to offer a particular prayer more than suffices to fulfill the requirement of making the niyah or intention for prayer. If one has made intention in ones heart to offer a particular prayer, does the wudu in preparation for the prayer, approaches the masjid or stands on the prayer mat in the direction of the qiblah to start their prayer, etc. There is absolutely no need for the believer to now verbally declare his intention for prayer! 

I hope this answers your question.