It is narrated from Humaid that Hasan (may Allah have mercy on him) was asked: Can a person make a bequest for his wealthy brother? He said: Yes, he can, even if that brother owns twenty thousand, then he said: or owns one hundred thousand, his wealth will not deprive him of this right.
Hadith Referenceسنن دارمي / من كتاب الوصايا / 3296