Hadith 17:425
Ibn Fudayl narrated to us, from Ash'ath, from al-Hasan, who said: "The polytheists are indeed unclean, so do not shake hands with them. Whoever shakes hands with them, let him perform ablution."
حدثنا بن فضيل عن أشعث عن الحسن قال إنما المشركون نجس فلا تصافحوهم فمن صافحهم فليتوضأ