Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
1- If it is an obligatory prayer, you ignore saying alhamdullilah when you sneeze.
2- In the a supererogatory prayer, it is fine to say alhamdullilah when you sneeze.
3- However, people should not reply and say yarhamukallah.
Watch this video to know the detailed answer given by Sheikh Yaser Birjas:
Do I Say Alhamdulillah When I Sneeze In Salah? | Shaykh Yaser Birjas
Q: Do I Say Alhamdulillah When I Sneeze In Salah?Everyone has been in a situation where they've sneezed during prayer. When this happens, does one say Alhamdulillah? We know saying it comes with great reward. Also, those responding to it gain reward. What is the ruling when this happens in prayer? SHARE & TAG YOUR FRIENDS!
Posted by Faith IQ on Wednesday, 25 April 2018
Almighty Allah knows best.
Source: Faith IQ.