قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ : " وَالَّذِي نَفْسُ مُحَمَّدٍ بِيَدِهِ، لَوْلا أَنْ أَشُقَّ عَلَى الْمُؤْمِنِينَ، مَا قَعَدْتُ خَلْفَ سَرِيَّةٍ تَغْزُو فِي سَبِيلِ اللَّهِ، وَلَكِنْ لا أَجِدُ سَعَةً فَأَحْمِلَهُمْ، وَلا يَجِدُونَ سَعَةً فَيَتَّبِعُونِي، وَلا تَطِيبُ أَنْفُسُهُمْ أَنْ يَقْعُدُوا بَعْدِي "
And the Messenger of Allah, peace and blessings be upon him, said: "By the One in Whose hand is my soul! If I did not fear hardship for the believers, I would never stay behind from any group fighting in the way of Allah. But I do not have enough means to mount all of them and take them with me, nor do they have enough mounts to ride with me, and nor do they like to stay behind after I have gone."
Related hadith on this topic