Does repeating "Yarhamuk Allah" (may Allah have mercy on you) to the sneezer twice constitute mockery of religion, and would the listener's laughter necessitate disbelief?

The statement "May Allah have mercy on you" said twice by the one who responds to a sneeze does not constitute mockery of religion, nor does laughing at the phrase lead to disbelief merely because of the laughter. However, it is necessary to adhere to the Sunnah in responding to a sneeze, which is for the one responding to say: "May Allah have mercy on you," and for the sneezer to reply: "May Allah guide you and rectify your affairs." One must be cautious of falling into doubt concerning disbelief (takfir), for whoever's Islam is established with certainty, it is not removed except by a certainty of equal strength.