Abdullah bin Umar reported,

I never heard Umar say of anything, "I suspect it is such and such," except that it turned out to be just as he suspected.While Umar was sitting one day, a handsome man passed by him. Umar said, "My judgment is mistaken, or else this man followed his old religion in the days of ignorance," or perhaps he said, "He was their soothsayer. Bring the man to me."The man was called over, and Umar said this to him. The man replied, "I have never seen anything like what has happened today, the way a Muslim man has been received."Umar said, "I insist that you tell me."The man said, "I was their soothsayer in the days of ignorance."Umar asked, "What is the most astonishing thing your female jinn ever brought you?"The man said, "One day, while I was in the marketplace, she came to me, and I could see terror in her face. She said, 'Have you not seen the jinn and their dismay, their despair after being cast down, and their attachment to the young camels and their saddle blankets?'"Umar said, "He speaks the truth. While I was sleeping near their idols, a man came with a calf and slaughtered it. Then a voice cried out, and I have never heard any crier with a louder voice, saying, 'Jalih! A successful command! An eloquent man declaring, There is no god but Allah!' The people sprang up. I said to myself, I will not leave until I know what lies behind this. Then the voice called again, 'Jalih! A successful command! An eloquent man declaring, There is no god but Allah!' I stood up, and not long after, it was said, 'This is a prophet.'"

Bukhari 3866

Sahih

حدثنا يحيى بن سليمان قال حدثني ابن وهب قال حدثني عمر أن سالما حدثه

عن عبد الله بن عمر قال

ما سمعت عمر لشيء قط يقول إني لأظنه كذا إلا كان كما يظن بينما عمر جالس إذ مر به رجل جميل فقال لقد أخطأ ظني أو إن هذا على دينه في الجاهلية أو لقد كان كاهنهم علي الرجل فدعي له فقال له ذلك فقال ما رأيت كاليوم استقبل به رجل مسلم قال فإني أعزم عليك إلا ما أخبرتني قال كنت كاهنهم في الجاهلية قال فما أعجب ما جاءتك به جنيتك قال بينما أنا يوما في السوق جاءتني أعرف فيها الفزع فقالت ألم تر الجن وإبلاسها ويأسها من بعد إنكاسها ولحوقها بالقلاص وأحلاسها قال عمر صدق بينما أنا نائم عند آلهتهم إذ جاء رجل بعجل فذبحه فصرخ به صارخ لم أسمع صارخا قط أشد صوتا منه يقول يا جليح أمر نجيح رجل فصيح يقول لا إله إلا الله فوثب القوم قلت لا أبرح حتى أعلم ما وراء هذا ثم نادى يا جليح أمر نجيح رجل فصيح يقول لا إله إلا الله فقمت فما نشبنا أن قيل هذا نبي

البخاري 3866صحيح
Contents
Reference
Commentary
Ayat
Collection
Sahih Bukhari
Book
Virtues of the Ansar
Chapter
Islam of Umar bin Khattab, may Allah be pleased with him
Numbering
Darussalam 3866
Bukhari 3866