Anas bin Malik رضي الله عنه narrated that:
أن رجلا من أهل البادية كان اسمه زاهر بن حزام أو حرام ، قال : وكان النبي صلى الله عليه وسلم يحبه وكان دميما ، فأتاه النبي صلى الله عليه وسلم يوما وهو يبيع متاعه ، فاحتضنه من خلفه وهو لا يبصره ، فقال : أرسلني ! من هذا ؟ فالتفت فعرف النبي صلى الله عليه وسلم ، فجعل لا يألو ما ألزق ظهره بصدر النبي صلى الله عليه وسلم حين عرفه ، وجعل النبي صلى الله عليه وسلم يقول : من يشتري العبد ، فقال : يا رسول الله ! إذا والله تجدني كاسدا ، فقال النبي صلى الله عليه وسلم : لكن عند الله لست بكاسد ، أو قال : لكن عند الله أنت غال
“There was a man from the people of the desert whose name was Zahir bin Hizam (or bin Haram). And he was loved by the Prophet صلى الله عليه وسلم – He was (also) not of a pleasant (facial) appearance. The Prophet صلى الله عليه وسلم came to him one day, while he (Zahir) was selling his goods (in the market) and embraced him (from behind) so that he (Zahir) could not see who it was [nb. in another narration he صلى الله عليه وسلم placed his hands over his eyes to stop him from looking behind]. Zahir asked: ‘Tell me, who is this?’, he turned and found it was the Prophet صلى الله عليه وسلم, so he continued to rub his back (and cling) onto the chest * (of the Prophet صلى الله عليه وسلم).
Upon this, the Prophet صلى الله عليه وسلم (held him and) said (in jest to those around him):
‘Who would like to buy a slave (from me)’?
He (Zahir) said:
‘O Messenger of Allaah, by Allaah you will find me to be a poor sell (i.e. I’ll be of no value)’.
The Prophet صلى الله عليه وسلم said:
‘But with Allaah you are not unsellable?’ [in another narration ‘But with Allaah you are valuable’].“
[Reference: Al-Bayhaqi, ‘Sunan al-Kubra’, 10/248 [found in Musnad Ahmad, Musnad Abi Ya’la and Bazzar with slight variations] – graded as saheeh by Ibn Katheer in ‘Al-Bidaayah’, 6/48; Ibn Hajar in ‘Al-Isaabah’, 1/542; Al-Haythami in ‘Majma az-Zawa’id’, 9/371 (#15979) and al-Albani in ‘Takhreej Mishkat al-Masabih’, 4815 (see also ‘Mukhtasar Shama’il’, 204)]
* This gesture of rubbing his back with the body of the Prophet صلى الله عليه وسلم was due to the barakah he hoped to attain.