Musnad Imam Shafi'i

It is narrated from Ibn Sirin, may Allah have mercy on him, that a man made a vow that when any of his children reached the age of weaning—such that he would wash milk, drink it himself, and give it to those with him—he would take him along and perform Hajj himself as well. One of the old man’s children came to know of this, and that man had become very old. So his son told the whole matter to the Messenger of Allah ﷺ. He said: “Indeed, my father has become very old, he does not have the strength to perform Hajj. Can I perform Hajj (as a substitute) on his behalf?” The Messenger of Allah ﷺ said: “Yes.”