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.
If the deceased did not leave any other heirs except a son and a daughter, then his inheritance should be divided between them by Ta’seeb (by virtue of having a paternal relation with the deceased and not having an allotted share, so they get what is left after the allotted shares have been distributed).
The male gets twice the share of the female as Allaah The Almighty Says (what means): {Allaah instructs you concerning your children [i.e. their portions of inheritance]: for the male, what is equal to the share of two females.} [Quran 4:11]
Therefore, the inheritance should be divided into three shares, the son gets two shares and the daughter gets one share.
Allaah Knows best.