All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
According to those who spoke about the permissibility of praying over a deceased Muslim who is absent (i.e. in another land), the basis of this is that the Prophet, sallallaahu ‘alayhi wa sallam, offered prayer over the Negus (of Ethiopia). Abu Hurayrah narrated that the Prophet, sallallaahu ‘alayhi wa sallam, announced the death of the Negus on the day on which he died. He went out with the people to the prayer area, organized them into rows and announced the Takbeer (i.e. saying "Allaahu Akbar") four times. [Al-Bukhari and Muslim]
Those who disagreed about the permissibility of offering prayer over an absentee did so because they regarded this as something specific to the Prophet, sallallaahu ‘alayhi wa sallam.
In addition to the permissibility of praying over an absentee, the basis of praying over the deceased is that it be done after washing and preparing the body. There is no difference between the absentee and the present in this respect. Therefore, whoever wants to prayer over an absentee must first determine if he was washed and prepared (i.e. shrouded). Then, he may pray over him.
Allaah Knows best.