What is the ruling on congratulating a non-believer on the occasion of the birth of a child?

It is permissible to congratulate a disbeliever on a newborn, but one must be cautious not to congratulate them on matters specific to their religion, such as holidays. A Muslim is prohibited from using phrases that imply honor or approval of their religion when congratulating them, unless the congratulation pertains to common matters. Imam Ahmad permitted congratulating them on marriage, a child, or the return of a traveler, but with caution regarding words that indicate approval of their religion. He also permitted visiting them when they are sick.