Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that he was sitting by the pulpit of the Messenger of Allah (peace and blessings be upon him) while he (peace and blessings be upon him) was addressing the people, when a man from the desert came to him (peace and blessings be upon him) and said: "O Messenger of Allah, what about the night prayer?" He (peace and blessings be upon him) said: "Yes, two (rak'ahs) by two. Then, when you fear that the dawn will overtake you, or that the dawn is about to come, pray one rak'ah; it will make the prayer you have offered odd (witr)."
Al-Muthanna (may Allah have mercy on him) narrates: We came to al-Qasim bin Muhammad bin Abi Bakr (may Allah have mercy on him) and asked him, and he narrated to us from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both), from the Prophet (peace and blessings be upon him), a hadith like the one Salim (may Allah have mercy on him) had narrated to us.
Imam al-Tabarani (may Allah have mercy on him) said: "No one narrated this hadith from Salim and al-Qasim except Abu Ubaydah."