As we know generally that Sunnah of the Prophet Muhammad SAWW is a pathway for whole human kind to follow in order to be successful in this world and hereafter. However, there are kinds of Sunnah in which a Muslim must distinguish in order to prioritize his/her actions. In order to understand the understand the place of Qiyamullail in the life of Prophet Muhammad SAWW, and what makes it sunnah for us, and a kind of Sunnah, it is imperative to understand what Sunnah is.

People think that Sunnah is to follow the every action of Prophet SAWW, but here we like to make it clear that every action of the Prophet Muhammad SAWW is not to be follow as Prophet SAWW performed. For example, the Tahajjud prayer was obligatory on Prophet SAWW to offer regularly (Daily) but we are not allowed to perform Tahajjum as obligation.

The same, Qiyamullail was an obligatory upon Prophet Muhammad SAWW, but he was given the option to spend half of the night, more or less, in performing His Qiyamullail. As Allah Subhana Wa Ta’ala says while addressing Prophet SAWW,
 

“O you who wraps himself [in clothing]. Arise [to pray] the night, except for a little. Half of it – or subtract from it a little. Or add to it, and recite the Qur’an with measured recitation.” (Surah Al-Muzzammil, 73:1-4)

Also in another place, Allah SWT emphasized that upon him SAWW,
 

“And from [part of] the night, pray with it (the Qur’an) as additional [worship] for you; it is expected that your Lord will resurrect you to a praised station.” (Surah Al-Israa, 17:79)

Therefore, that obligation of Qyam ul Layl was special of our Beloved Prophet Muhammad SAWW as many of Sunnah of Prophet Muhammad SAWW were special for him SAWW alone.