Abd al-Rahman bin Jubayr bin Nufayr narrates from his father, who said: We sat with Sayyiduna al-Miqdad bin al-Aswad (may Allah be pleased with him) in Damascus; he was (sitting) on a chest, and he had nothing to spare beyond it. A man said to him: If you stayed back from the campaign this year, it would be better. He said: Al-Buhuth, that is, Surah al-Tawbah, has held us to it, meaning Surah al-Tawbah does not let us sit back, for Allah Almighty says: "Go forth in the path of Allah, light or heavy, whatever your state." [Surah al-Tawbah: 41] So I find myself light.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17800