From the 2003 Laws Of Cricket
Law 2
9. Batsman leaving the field or retiring
A batsman may retire at any time during his innings. The umpires, before
allowing play to proceed, shall be informed of the reason for a batsman
retiring.
(a) If a batsman retires because of illness, injury or any other unavoidable
cause, he is entitled to resume his innings subject to (c) below. If for any
reason he does not do so, his innings is to be recorded as 'Retired - not
out'.
(b) If a batsman retires for any reason other than as in (a) above, he may
only resume his innings with the consent of the opposing captain. If for any
reason he does not resume his innings it is to be recorded as 'Retired -
out'.
(c) If after retiring a batsman resumes his innings, it shall be only at the
fall of a wicket or the retirement of another batsman.
--
George
"Strike me down while you can, but it won't make your dried up ovaries any
more fertile." - Eric Cartman - 3 May 2006