(aap logon kay questions ka answer Islam section main bhi kiya hai.. jis nay udhar dekhna hai wo udhar dekh lay......)

salam
Ghadir, Makka or Madina kay darmiyan aik jaga ka naam hai. 18 zil'hajj ko shian'ay haider bai'had khushi ka din samjhte hain isi munasbat say is din ko Eid'ay Ghadeer kaha jata hai.
lafz "Ghadir Khumm" aik jaga ka naam hai jo mojooda Al-juhfa kay paas hai, khumm is jaga aik kun'wain ka naam tha. jab qafla is jaga pohncha to quran ki (Quran 5:67) ayet nazil hui.
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"O Apostle! Deliver what has been sent down to you from your Lord; and if you don't do it, you have not delivered His message (at all); and Allah will protect you from the people ..." (Qur'an 5:67)
is jaga rasool allah muhammad (sa) nay akhri hajj say wapsi par paraao kiya tha or apnay sath qaafla main shamil taqreeban sawa lakh logo'n ko ruknay ka kaha. pathro'n or oonto'n ki madad say us maidan main aik mimber banwaya. jab qaflay main shamil wo log jo peechay thay wo bhi pohnch gaye to nabi paak (sa) nay sawa laakh kay majma say kitaab kiya. jis ki detail history ki books say mil sakti hai.. apnay is khitaab kay akhir main rasool allah nay Hazrat Ali ka hath pakar kar buland kiya or yai tareekhi jumla kaha jo kay oopar image main hai...
"man kunto mola, fahaza ali mola"
us ki urdu translation yai hai...
"jis jis ka main mola, us ka Ali mola."
is kay baad doosra tareekhi jumla kaha..
"aye khuda, jo is say piyar kare tu us say piyar kar or jo is kay khilaf hon tu us kay khilaf ho"
rasool allah nay majma main shamil aik aik fard ko Ali ki bai'et karne ko kaha or har aik nay ki.tamam sahaaba or hujjaj karaam nay Ali ki bai'et ki or un ko tamam momneen ka ameer ban'ne ki mubarkbad di.
Hazrat Ali kay rasool allah kay janasheen or khalifa ban'ne ki khushi main shian'ay haider 18 zilhajj ko khushi ka izhaar karte hain.
ab aatay hain is baat ki taraf kay yai sab kahan likha hai.Ghadir Khumm or Ali ki wilayet ka waqiya shia history ki taqreeban har book main hi mile ga or jahan tak talluq hai ahl'ay sunnat kitabon ka to tamam aisi kutab jis main rasool allah kay akhri hajj ki details hain us main Ghadir ka waqiya shamil hai..jin main about 185 ahadees, tareekh, tafseer etc. ki list idhar hai..
http://www.al-islam.org/ghadir/books.aspmaslan sanan, tareekh'ay kabir, Kitáb al-Sunnah , Manáqib `Alí b. Abí Tálib, Hilyat al-Awliyá' , Ta'ríkh Baghdád , bukhari ki books, ibn maja ki books, tirmizi ki books ewaghera.
More detail here.
http://www.al-islam.org/ghadir/http://shiaonline.wordpress.com/tag/ghadir-khum/wikipedia par is ka link yai hai,
http://en.wikipedia.org/wiki/Ghadir_Khum