It hasn't come out in the anime yet but is relased in Japan's version of the manga, Volume 30.
Miroku tells Sango his feelings. That to him, she is a special girl, and he has never respected a female like he has ever respected her. But he sees her as a companion, a friend to fight alongside. She blushes alot and says something, then he says that after the battle with Naraku, if they are both still alive, if she would bear his child. SANGO SAYS YES. Miroku is estatic, saying things like, "You'll bear them? 10, or even 20?" Kagome and Inuyasha are in the bushes spying. Kagome says, "Kyaa! He proposed!" Sango is happy, and asks him if he'll never cheat on her again, but recieves no answer...
website where it can be found (translated): http://www.anzwers.org/free/mirokusango/chapter_292.htm
Submitted by Sruthi/Rachel