What color is the blood that he is passing in the stool - blackish, reddish? is the entire stool blackish or are there only streaks of blood on the stool?
If the blood color is blackish, then he is bleeding from the ulcer in his stomach. This needs emergency care to control the bleeding. Please take him to the ER as early as possible.
Meanwhile give him sips of cold water to help the open blood vessels to constrict to some extent and decrease the bleeding. Thsi will not however stop the bleeding and he needs medical attention as early as possible.
I hope this helps.
Let me know if you need more input. If not, please click on the green"Accept" button on this page. A positive rating and adding a bonus will be warmly appreciated.