Kommentar zu Bereschit 25:4

ויתן, he distributed his wealth during his lifetime in order to forestall quarrels about his inheritance after his death. כל אשר לו ליצחק, he had appointed Yitzchok as his heir as he had been commanded to do by G’d when Ishmael had been expelled. (21,12) Anything the other sons received was in the nature of “gifts,” not “inheritance.”