Sahih Bukhari Volume 4, Book 56, Hadith 2835

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مُحَمَّدٍ، حَدَّثَنَا مُعَاوِيَةُ بْنُ عَمْرٍو، حَدَّثَنَا أَبُو إِسْحَاقَ، عَنْ حُمَيْدٍ، قَالَ سَمِعْتُ أَنَسًا ـ رضى الله عنه ـ يَقُولُ خَرَجَ رَسُولُ اللَّهِ صلى الله عليه وسلم إِلَى الْخَنْدَقِ فَإِذَا الْمُهَاجِرُونَ وَالأَنْصَارُ يَحْفِرُونَ فِي غَدَاةٍ بَارِدَةٍ، فَلَمْ يَكُنْ لَهُمْ عَبِيدٌ يَعْمَلُونَ ذَلِكَ لَهُمْ، فَلَمَّا رَأَى مَا بِهِمْ مِنَ النَّصَبِ وَالْجُوعِ قَالَ : اللَّهُمَّ إِنَّ الْعَيْشَ عَيْشُ الآخِرَهْ فَاغْفِرْ لِلأَنْصَارِ وَالْمُهَاجِرَهْ‏.‏ فَقَالُوا مُجِيبِينَ لَهُ : نَحْنُ الَّذِينَ بَايَعُوا مُحَمَّدًا عَلَى الْجِهَادِ مَا بَقِينَا أَبَدًا

Narrated By Anas : Allah's Apostle went towards the Khandaq (i.e. Trench) and saw the Emigrants and the Ansar digging in a very cold morning as they did not have slaves to do that for them. When he noticed their fatigue and hunger he said, "O Allah! The real life is that of the Here-after, (so please) forgive the Ansar and the Emigrants." In its reply the Emigrants and the Ansar said, "We are those who have given a pledge of allegiance to Muhammad that we will carry on Jihad as long as we live."