What is the prayer that was obligatory upon the Prophet but voluntary for the Ummah?

The scholars differed regarding the obligation of Qiyam al-Layl (night prayer), Witr, Salat al-Duha (forenoon prayer), and the two rak'ahs of Fajr specifically for the Prophet, peace be upon him, to the exclusion of the Ummah. Some of them hold that he was uniquely obligated to perform some of these, while others hold that he was uniquely obligated to perform all of them. The Malikis, Shafi'is, and Hanbalis considered some of these prayers obligatory upon him, to the exclusion of the Ummah, with some disagreement regarding certain ones like Qiyam al-Layl and Salat al-Duha, and the abrogation of the obligation of Tahajjud.