13].Surah Ar-Ra'd [The Thunder] : Ayat 38-39

Ayat 38. And indeed We sent Messengers before you (O Muhammad  [SAWW](PBUH), and made for them wives and offspring. And it was not for a Messenger to bring a sign except by Allah's Leave. (For) each and every matter there is a Decree (from Allah).  

Ayat 39. Allah blots out what He wills and confirms (what He wills). And with Him is the Mother of the Book (Al-Lauh Al-Mahfûz) 

Hazrat Ibn `Umar (May Allah be pleased with them) reported: We were talking about the Farewell Pilgrimage without knowing what was it when Messenger of Allah  [SAWW](PBUH) was also present. He  [SAWW](PBUH) stood up and recited the Praise and Glorification of Allah. He then gave a detailed account of Ad-Dajjal and said, 'Every Prophet sent by Allah had warned his people against his mischief. Nuh (PBUH) )warned his nation and so did all the Prophets after him. If he (i.e., Ad-Dajjal) appears among you, his condition will not remain hidden from you. Your Rubb is not one-eyed, but Ad-Dajjal is. His right eye is protruding like a swollen grape. Listen, Allah has made your blood, and your properties as inviolable as of this day of yours (i.e., the Day of Sacrifice), in this city of yours (i.e., Makkah), in this month of yours (i.e., Dhul -Hijjah). Listen, have I conveyed Allah's Message to you?'' The people replied in affirmative. There upon he said, "O Allah, bear witness.'' And he repeated it thrice. He  [SAWW](PBUH) concluded: "Do not revert after me as infidels killing one another".

[Al-Bukhari]. Book 04, Chapter 55, Hadith # 553]. 

Lesson : as mentioned above in Surah Ar-Ra'd Ayat 38. "And indeed We sent Messengers before you (O Muhammad  [SAWW](PBUH)," This Hadith brings out the following three points: (1). Some marks and signs of pseudo-Messiah (Al-Masih Ad-Dajjal) are mentioned to warn the believers against his mischief. (2). The lives and properties of Muslims are inviolable for each other. In other words, it means that each of them is a protector and guardian of the life, property and honour of the other. (3). Internal war among the Muslims is a great crime and can even lead to infidelity (Kufr). May Allah save us all from it.