You can pray one Rak'ah of witr

The 'ahnaaf alone have forbidden praying one Rak'ah of witr based on the following weak hadith while all other schools have permitted it based on authentic hadith

أن رسول الله - صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ - نهى عن البتيراء أن يصلي الرجل واحدة يوتر بها

The only difference between the Maaliki and the Shaafi'i and Hanaabilah is that the Maaliki say that you can pray one Rak'ah of witr but have to precede it by praying an even number of Rak'ah. The Shaafi'i and Hanaabilah do not have this stipulation.