Question 53: Are the following two statements Hadeeths or Athar (narrations from the Companions): “May Allaah be merciful to the one who knows his own limits” and “Much laughter kills the heart”? Who are their narrators and to what extent are they Saheeh (authentic)?
Answer: Research and verification show that the phrase that you have mentioned in the question reading: “May Allaah be merciful to the one who knows his own limits” has no origin in any of the variant narrations. As far as we know, such a phrase is not found in the authentic Books of Hadeeth scholars and it is not reported from any of the Sahaabah (Companions of the Prophet) or the Taabi`oon (Followers, the generation after the Companions of the Prophet). It is a commonly used phrase whose sayer is unknown… read more here.