Is there any hadith which says that it is prescribed to say Amin when entering the mosque?
Supplications for entering the mosque include: “Allahumma iftah li abwaba rahmatika (O Allah, open to me the gates of Your mercy).” “ A`udhu Billah il-`Azim wa bi wajhihi’l-karim wa sultanihi’l-qadim min ash-shaytan ir-rajim (I seek refuge with Allah the Almighty and His noble countenance and His eternal power from the accursed Shaytan).” When exiting the mosque, one should say: “ Allahumma inni as’aluka min fadlika (O Allah, I ask You of Your bounty).” Regarding what the questioner said about it being recommended to say Amin when entering the mosque, there is no such report from the Prophet (blessings and peace of Allah be upon him) or from his Companions (may Allah be pleased with them), and we have not come across any of the scholars who said that.