Musnad Ahmad 25:412

Abu Mu'awiyah narrated to us, Hajjaj narrated to us, from Abu al-Zubayr, from Tawus, from Ibn Abbas, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The *'umra* (life-gift) belongs to the one to whom it was given. The *ruqba* (contingent gift) belongs to the one to whom it was granted. And the one who takes back his gift is like the one who returns to his vomit."