Hammad bin Zaid narrated this: The mention of touching the armpit was made before Ayyub, so he said: "Some armpits are such that after touching them, one should perform ghusl (ritual bath)."
Hadith Referenceسنن الدارقطني / كتاب الطهارة / 552
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 551»