Comentario citado sobre Números 32:5

כל אשר יתן ממנו, “all that he gives of it, etc.” the Torah employs the masculine mode here although the word בהמה, the subject here, is a beast in the feminine mode. This is not a unique occurrence, as other such examples are to be found in Leviticus 6,8, where the pronoun ממנו, which is masculine, is used in reference to the noun מנחה, which is feminine; two more such anomalies occur in Numbers 32,5 and Genesis 13,6.

Alternatively, the words צדקת ה׳ עשה may refer to Gad who acted in a manner which G'd considered as righteous when this tribe undertook to join the main body of the Israelites and to remain with them until completion of the wars of conquest. If we were to consider the matter on a purely legal basis, i.e. their obligations vis-a-vis G'd, the tribe of Gad was not obligated to do this. They had received their inheritance in the place of their choosing as they had argued at the time in Numbers 32,5. If that had not been so G'd would never have consented for them to remain on that territory. As a result, the fact that they crossed the Jordan as the vanguard of the Israelite army was an act that was considered as righteousness for them. However, it was an act of righteousness only vis-a-vis G'd. Vis-a-vis their compatriots it was a sacred duty, not something for which they deserved a reward. The wording צדקת השם עשה is very appropriate then.