Lady Aisha (may Allah be pleased with her) narrates from the Noble Prophet (peace and blessings be upon him) that he said: "When the ablution of any one of you breaks during prayer, he should place his hand on his nose and leave the prayer."
Hadith Referenceصحيح ابن خزيمه / جماع أبواب الصلاة على البسط / 1019