This research deals with negation as a grammatical phenomenon of Arabic sentences through the analysis of the Prophetic hadith There should be no harming nor reciprocating harm which is taken from the book A Collector of Sciences and Wisdom by Ibn Rijab Al Hanbali ( d.795H). The paper focuses on the particle of negation categorical Laa from a syntactic and semantic perspective as viewed by Arab grammarians. The study shows that this grammatical phenomenon has its syntactic and semantic impact on the Prophetic hadith. Syntactically it changes the word - inflection of its subject and predicate . Semantically, it leads to a generalization that initially there should be no harming and if this harm exists there should on reciprocating of this aggression. The paper also reveals that the scholars have different opinions on the terms " AL - Dharar ( harm ) and Al - Dhirar( reciprocating harm) .Moreover they differ with respect to the two different forms of AL - Dharar. The first form AL Dhur where the last sound " r "germinates indicates harm The second form Dharar means disability .This last meaning is not intended by the hadith.