What is the Meaning of this hadith in Tirmidhi

What is the meaning of The hadith: Masruq narrated that : he asked Aishah about the Witr of the Prophet. She said: He would perform Witr during all of the night; (either) its beginning, its middle, or its end. So when he died, his Witr ended, during the approachof As-Sahar. So my question is What does it mean "so when he died"