The Life of the Buddha: The Appointment of Ananda.
During the first twenty years of the Buddha's life, his personal attendants were not such permanently. The Brethren took it by turns to carry the Master's bowl and cloak, and he did not favour one more than another. But one day he addressed the Brethren and said: "O Bhikkhus, I am now advanced in years; and some Bhikkhus, when they have been told 'Let us go this way,' take another way, and some drop my bowl and cloak on the ground. Do ye know of a Bhikkhu to be my permanent body-servant?" Then the venerable Sariputta arose and said: "I Lord, will wait upon thee." Him the Exalted One rejected, and Moggallana the Great, also. Then all of the foremost disciples said: "We will wait upon thee." Only Ananda remained silent; for he thought "The Master himself will say of whom he approves." Then the Exalted One said: "O Bhikkhus, Ananda is not to be urged by others; if he knows it of himself, he will wait upon me." Then Ananda stood up and said: "If, Lord, thou wilt refuse me four things, and grant me four things, then I will wait on thee." Now the four things that Ananda wished to be denied were special favours, for he did not wish it to be said that his service was undertaken for the sake of clothes, or good fare, or lodging, or that he might be included in invitations. And the four boons that he desired were that the Buddha would accept any invitation received through Ananda, that he would be easy of access to such as Ananda should bring to speak with him and to Ananda himself, and that he would repeat to Ananda such doctrines as he desired to hear again; for Ananda did not wish it to be thought that the Buddha made no account of him, nor that men should say that the Buddha's immediate attendant was not well versed in the doctrine. All these boons were granted by the Blessed One, and thenceforward until the day of his death, Ananda remained the permanent attendant of the Buddha. It was not, however until after the Buddha's death that Ananda attained to Arahatta.