Hadith 1080
Sayyiduna Ali narrates that the Messenger of Allah (peace and blessings be upon him) has performed Witr in every part of the night: in the early part of the night, in the middle of the night, and also in the last part of the night.
Hadith 1081
Sayyiduna Abdullah bin Qais narrates that he asked the noble wife of the Prophet, Sayyidah Aisha (may Allah be pleased with her), how the Messenger of Allah (peace and blessings be upon him) used to perform Witr—did he offer it at the end of the night or at the beginning of the night? She replied that he (peace and blessings be upon him) used to offer it in every part. Sometimes he would offer it at the beginning of the night, and sometimes he would perform it in the last part of the night. So I said, all praise is due to Allah who has placed ease and flexibility in this matter.