936. hadíth
وَ فِي خَبَرٍ آخَرَ: «مُدّاً مِنْ طَعَامٍ أَوْ كَفَّيْنِ». والأولى أن لا يحك المحرم رأسه إلا حكا رفيقا بأطراف الأصابع.
In another narration: "A mudd of food or two handfuls." It is preferable that the person in the state of ihram does not scratch their head except gently, using the tips of their fingers.