Reference: Fataawa Ramadhaan – Volume 2, Page 541, Fatwa No.519
Fataawa as-Siyaam – Page 87
Question: Does the swallowing of saliva break the fast?
Response: There is no harm in swallowing saliva, however, it is disliked to gather saliva. So, the gathering of saliva [in the mouth] and then swallowing it is severely disliked, even if it does not break the fast.