Fiqh-us-Sunnah - 1.143

Hadith 1.143.1

Lengthening the first rak'ah of the morning prayer

The Prophet, upon whom be peace, would make the first rak'ah of the morning prayer longer than the second. At times, he would continue to prolong his recitation until he heard no more footsteps (of the people coming to catch the prayer). He made the morning prayer the longest of his (obligatory) prayers. This is because its recitation is witnessed by Allah and the angels. It is also stated that it is witnessed by both the angels who record the daytime deeds and those who record the nighttime deeds.
Whether it is Allah and His angels or His angels alone who witness that time, or does it continue until the morning prayer is over or until the sun rises cannot be said with certainty, though both of the statements are correct.
Furthermore, since the morning prayer has the least number of rak'ah, the recitation is prolonged to compensate for it. It is prayed right after sleep. As such, people are well rested. Also, it occurs before they have engaged themselves in their livelihood and other worldly affairs. The spirit as well as the body is responsive to the words of Allah. This makes the recital easier to ponder over and comprehend. Also, prayer is the basis and the first of all works. Therefore, it is preferred to prolong the recital of the morning prayer.
This would be recognized by one who is familiar with Islamic law and its aim, purpose and wisdom.