Are the third unit of prayer shorter than the second, and the fourth shorter than the third?

The Sunnah indicates the desirability of prolonging the recitation in the first rak'ah more than the second. The reason for this is that one's energy is higher in the first, or due to the Istiftah supplication (opening supplication). Muslim narrated from Hafsa that the Prophet, peace and blessings be upon him, used to recite the surah slowly and distinctly, so that it would be longer than another surah that was longer than it. As for the third and fourth rak'ahs, it has not been reported from the Prophet, peace and blessings be upon him, that he differentiated between them in length, nor is it sunnah to recite more than Al-Fatihah in them.