Sahih Bukhari Volume 001, Book 008, Hadith Number 452.
Narated By 'Aisha : On the day of Al-Khandaq (battle of the Trench' the medial arm vein of Sa'd bin Mu'ad was injured and the Prophet pitched a tent in the mosque to look after him. There was another tent for Banu Ghaffar in the mosque and the blood started flowing from Sa'd's tent to the tent of Bani Ghaffar. They shouted, "O occupants of the tent! What is coming from you to us?" They found that Sa'd' wound was bleeding profusely and Sa'd died in his tent.