It was narrated to us by Moḥammed bin Ibrāhīm رحمه الله, who said – it was reported to us by Aḥmed bin Moḥammed al-Hamdāni, from ʿAlī bin al-Ḥassan bin ʿAlī bin Fadhāl, from his father:1

From Abī al-Ḥassan ʿAlī bin Mūsa al-Ridha عليه السلام whereupon a man from the people of Khorasān said to him: Oh son of the Messenger of Allāh, I saw the Messenger of Allāh صلى الله عليه وآله in my dream, as if he was saying to me: ‘What will be your condition when a part of me will be buried in your land, and you are made to be protectors of my trustee, and my star will be hidden amongst your increased numbers?’
Al-Ridha عليه السلام said: I am the one that will be buried in your land, and I am the one that is a part of your prophet, and I am the one who is the trustee and the star. Unquestionably, whoever visits me while having cognizance of what Allāh, Blessed and High, has made obligatory in regards to my rights and obedience – then my fathers and I will be his intercessors on the Day of Judgement. Whoever we are the intercessors of, he will be saved even if upon him is the like of the heavy burden of sins of all jinn and man. Indeed my father narrated to me, from my grandfather, from his father عليهم السلام that the Messenger of Allāh صلى الله عليه وآله said: ‘Whoever sees me in his dream then he has indeed seen me,2 because Shayṭān cannot manifest himself in my image, nor in the image of anyone of my successors, nor in the image of anyone of their Shiʿa. Indeed a truthful vision is one portion from the seventy portions of prophethood.’

1. Al-Shaykh Hādi al-Najafi says this ḥadīth has a reliable (muwathaq) chain [Mawsūʿat al-Aḥādīth ahl al-Bayt, Volume 4, Page 100]. Al-Moḥsini also states the chain is reliable, although states there needs to be much discussion regarding its contents [Mashraʿat Biḥār al-Anwār, Volume 2, Page 481]. We see no issues with its contents.
2. Whoever sees me in his dream then he has indeed seen me: Ḥaydar Ḥubb Allāh says – this requires a long discussion. Indeed some of our scholars have weakened this narration, from memory such as al-Sayed al-Murtadha, while others, like al-ʿAllamah al-Majlisi, tried to anagogically interpret it and limit it to certain instances.

حدثنا محمد بن إبراهيم ( رحمه الله ) ، قال : أخبرنا أحمد بن محمد الهمداني ، عن علي بن الحسن بن علي بن فضال ، عن أبيه ، عن أبي الحسن علي بن موسى الرضا ( عليه السلام ) أنه قال له رجل من أهل خراسان : يا بن رسول الله ، رأيت رسول الله ( صلى الله عليه وآله ) في المنام كأنه يقول لي : كيف أنتم إذا دفن في أرضكم بضعتي ، واستحفظتم وديعتي ، وغيب في ثراكم نجمي ؟ فقال له الرضا ( عليه السلام ) : أنا المدفون في أرضكم ، وأنا بضعة من نبيكم ، وأنا الوديعة والنجم ، ألا فمن زارني وهو يعرف ما أوجب الله تبارك وتعالى من حقي وطاعتي ، فأنا وآبائي شفعاؤه يوم القيامة ، ومن كنا شفعاؤه نجا ولو كان عليه مثل وزر الثقلين الجن والإنس . ولقد حدثني أبي ، عن جدي ، عن أبيه ( عليهم السلام ) أن رسول الله ( صلى الله عليه وآله ) قال : من رآني في منامه فقد رآني ، لان الشيطان لا يتمثل في صورتي ، ولا في صورة أحد من أوصيائي ، ولا في صورة أحد من شيعتهم ، وإن الرؤيا الصادقة جزء من سبعين جزءا من النبوة .