There are different sayings regarding the phlegm or congestion that drips from the head into the throat. According to Imam ash-Shafi^iyy if the phlegm reached to the part of the throat above where the exit of the letter ha’ is, and the person swallowed it, this would invalidate his fasting. However, according to Imam Abu Hanifah, even if the phlegm reached to the tongue and the person swallowed it, his fasting is not invalidated, as long as he does not swallow it after separating from his mouth.