Do not harm and do not be a cause of harm
Abu Sa’eed al-Khudree (radi Allahu anhu) said that the Messenger of Allah (sal Allahu alaihi wa sallam) said: “Do not harm and do not be a cause of harm.”
[Hadith Hasan related by Ibn Maajah and ad-Daaraqutnee]
His statement, “Do not harm” i.e. harm is prohibited in the legislation. “And do not be a cause of harm” i.e. to one who harms you.
The difference between the two is that harm occurs without being intentional and causing harm occurs intentionally. The Prophet (sal Allahu alaihi wa sallam) has prohibited both affairs, and causing harm is worse than harm because causing harm occurs intentionally as we have stated.
An example of that, if a person had a neighbour and that neighbour watered his tree causing the water to flow from the tree to the house of the other neighbour; but without being intentional and possibly without him knowing, then it is obligatory that he cease this harm. If the owner of the tree said after learning about it, ‘I did not intend any harm.’ We say to him, even if you did not intend (any harm, you still must cease it) because harm is prohibited in the legislation.
As for causing harm, if the neighbour purposely causes harm to the other neighbour so that water flows over to his house and other similar things; all of this is prohibited in the legislation. The scholars have extracted many issues from this hadith regarding the neighbour and other than that, and what is more excellent than a person reviewing what the scholars have mentioned about righteousness and the rights of the neighbour?
And Allah Knows Best!