Couplets are a part of China traditional culture. There was no such custom in the Arabian Peninsula during the period of Mu Sheng (peace and blessings be upon him), and of course there is no such custom now. Because Arabic is written horizontally, it is not convenient to write in the form of vertical couplets (although some Muslims in China have tried to write some Arabic characters in the form of "square characters" and write vertical couplets), and Muslims have not traditionally celebrated the Spring Festival, so there is no need to post couplets.

In China, Muslims have inherited this tradition and generally don't put up couplets during the Spring Festival to show their differences from the customs of the Han nationality. Couplets will be posted in front of some mosques, and the contents are mostly words praising the Lord and sanctifying saints.

As far as I know, there is no sermon with couplets.