Allah, the Blessed and Exalted, said concerning jihad: "There is no blame upon the weak, nor upon the sick, nor upon those who find nothing to spend, as long as they are sincere to Allah and His Messenger. There is no ground (of reproach) against the doers of good, and Allah Almighty is Most Forgiving, Most Merciful." [Surah al-Tawbah: 91]
To the end of the three verses.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / Q17813