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 is His slave and Messenger.
If the deceased did not leave any other heir except his parents, then his mother gets one third of the inheritance as her legal share as Allaah Says (what means): {But if he had no children and the parents [alone] inherit from him, then for his mother is one third.}[Quran 4:11] The remainder will be given to the father by Ta’seeb (by virtue of having a paternal relation with the deceased and not having an allotted share, so the heirs by right of Ta’seeb get what is left after the allotted shares have been distributed) as the Prophet said: “Give the prescribed share of inheritance to those who are liable for it and the remainder [of it] is for the nearest male blood relative." [Al-Bukhari and Muslim]
Therefore, the inheritance should be divided into 3 shares, the mother gets one-third, which is one share, and the father gets two shares.
Allaah Knows best.