Son of man and daughter of woman

Ibn Qudaamah said in al-Mughni:

If a man has a son from [a woman (i.e. an ex-wife)] other than his wife [who he is now married to] and she has a daughter from [a man (i.e. ex-husband)] other than him (or if he has a daughter and she has a son), then it is permitted for these two [i.e. son and daughter] to be married to one another according to the masses from among the Jurists. 

ولو كان لرجل ابن من غير زوجته، ولها بنت من غيره، أو كان له بنت، ولها ابن، جاز تزويج أحدهما من الآخر. في قول عامة الفقهاء