Maymuna bint Harith (r.anha)
The real name of Hz. Maymuna was “Barra”. One of her sisters, Ummu’l-Fadl was married to Hz. Abbas, the maternal uncle of the Prophet and her other sister Asma was married to Hz. Jafar, the cousin of the Prophet. The Messenger of Allah called these three sisters "believing sisters". When Hz. Maymuna's husband died, she became a widow. Hz. Abbas hoped that the Prophet would marry Hz. Maymuna. Therefore, whenever he met the Prophet, he would praise her and mention her high ethics and virtues.
The Prophet was on the way to Makkah for umrah. When had a break near Juhfa, Hz. Abbas approached the Prophet and asked him to marry Hz. Maymuna:
“O Messenger of Allah! Maymuna bint Harith is a widow now. Will you marry her?” The Prophet accepted his uncle's request. His uncle became very happy when he heard it.
Hz. Maymuna also became very happy when the Prophet accepted to marry her. When she heard the news, she was on a camel. She expressed her happiness by saying, “The camel and the one on it belong to the Messenger of Allah.”
Hz. Abbas married Hz. Maymuna off to the Prophet in the 7th year of the Migration in return for 400 dirhams as mahr. It was the last marriage of the Prophet (pbuh).
Hz. Maymuna died at the age of 80 in the 56th year of the Migration.
May Allah be pleased with her! 
 Tabaqat, 8: 120, 123; al-Isaba, 4: 412-413.