عن إبن عمر قال إذا توضأ الرجل ومس ابطه أعاد الوضوء
السنن الكبرى للبيهقي
Ibn Umar said: “If a man does ablution but then touches his armpit, he has to do ablution again.”
The Larger Compilation of Stories [Al-sunan Al-kubra] by Al-Bayhaqi