Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) saw a man on whose foot there was a spot that water had not reached. He (may Allah be pleased with him) said: Will you attend the prayer with this ablution? He said: O Commander of the Believers, the cold is severe, and I have nothing to protect me from it. He (may Allah be pleased with him) softened towards him after he had been about to punish him, and said: Wash the part of your foot that you left, and repeat the prayer. And he ordered that a woollen garment be given to him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 396