Sayyiduna Ka'b bin Ujrah (may Allah be pleased with him) said concerning this verse: "Then a ransom of fasting, or charity, or a sacrifice" [Surah al-Baqarah: 196]: I was carried to the Messenger of Allah (peace and blessings be upon him) while lice were falling over my face, and he (peace and blessings be upon him) said: "I did not think that the affliction had reached with you the extent that I see. Do you have a sheep?" I said: "No." He (peace and blessings be upon him) said: "Then fast three days, or feed such-and-such a number of poor people, half a sa' of wheat for each poor person."
Hadith Referenceالمعجم الكبير للطبراني / باب الكاف / 16349