Rav Menachem Mendel Alter, the son of the Sfas Emes and Rav of a place called Pabience, was in Aushwitz and asked for someone to bring him water. He promised his portion in Olam Haba for anyone who brings the water to him. The people were sure that he was so thirsty that he felt he would die if he didn't get some water and was willing to offer his portion in Olam Haba in order to fulfill the mitzva of "Vi-nishmartem meod linafshoseichem".
We he received the water he used it to ...... wash netilas yadaim so that he could say vidui and die in purity.
[Related by HaGaon Rav Chaim Kreizwerth ztz"l Mayim Chaim Page 126. The Rav compared this spiritual heroism to that of Rebbe Akiva].