Sahih Bukhari | Volume 5 | Hadith Number 425
Narrated by Anas
Allah's Apostle went out towards the Khandaq (i.e. Trench) and saw the Emigrants and the Ansar digging the trench in the cold morning. They had no slaves to do that (work) for them. When the Prophet saw their hardship and hunger, he said, 'O Allah! The real life is the life of the Hereafter, so please forgive Ansar and the Emigrants." They said in reply to him, "We are those who have given the Pledge of allegiances to Muhammad for to observe Jihad as long as we live."