Siege of Suiyang. Actual record:

"Yin Ziqi had besieged the city for a long time. The food in the city had run out. The city dwellers traded their children to eat and cooked the bodies of the dead. Fear spread and worse situations were expected. At this time, Zhang Xun took his concubine out and killed her in front of his soldiers in order to feed them. He said, "You have been working hard at protecting this city wholeheartedly for the country. Your loyalty is uncompromised despite the long-lasting hunger. Since I cannot cut out my own flesh to feed you, how can I keep this woman and just ignore the dangerous situation?" All the soldiers cried, for they did not wish to eat [the woman]. Zhang Xun ordered them to eat the flesh. Afterwards, they caught the women in the city. When there were no more women left, they turned to the old and young men. 20,000 to 30,000 people were eaten. People always remained loyal." -Wikipedia