Ruling on having chewing gum in one’s mouth when praying
Question

                What is the ruling on having gum in the roof of one’s mouth when praying? Does this invalidate prayer?
Praise be to Allah. 
          Every Muslim must fear Allaah and show respect towards 
          Him. When he stands in prayer before Allaah, he must stand in a manner 
          of humility and submission to Allaah, keeping far away from everything 
          that may corrupt or invalidate his prayer, distract his mind, or keep 
          him from focusing on the prayer. He must avoid anything that goes against 
          respect and good manners. 
 
          For a worshipper to have chewing gum in his mouth is 
          undoubtedly incompatible with fear and respect of Allaah, and with humility 
          before Him. It causes a lot of movement in the mouth.
 
          With regard to the ruling on having chewing gum in one’s 
          mouth when praying:
Ibn Qudaamah said: 
          If he has anything in his mouth that can dissolve, such as sugar, and 
          any part of it dissolves, and he swallows it, then his prayer is invalidated, 
          because he has eaten.
 
          (al-Mughni, part 1, p. 400)
According to the Hanafis, 
          Maaliks and Hanbalis, it is also makrooh to put anything in his mouth 
          even if that does not prevent him from reciting, because that distracts 
          his mind. The Hanafis stated that if this thing does not dissolve then 
          it is makrooh; if it does dissolve, such as sugar in his mouth, then 
          this invalidates his prayer if he swallows it after it has dissolved.
 
          (al-Mawsoo’ah al-Fiqhiyyah, part 27, p. 117)
 
          And they stated that if he has sugar in his mouth, and 
          it dissolves and he swallows it deliberately, knowing that that is forbidden, 
          or because he did not make any effort to learn, then his prayer is invalid. 
          They also stated that his prayer becomes invalid if he chews it, if 
          it is a lot, even if nothing reaches his stomach.
 
          Al-Majd said: if he brings out something substantial 
          that is between his teeth and swallows it, then his prayer becomes invalid 
          in our view. They stated that swallowing something that has dissolved, 
          such as sugar, is like eating.
 
          Al-Mawsoo’ah al-Fiqhiyyah, 
          part 27, p. 125