It is narrated that Imam Muhammad al-Baqir said and others have also related from reliable chains, especially Thalabi in his tafsir that one day the holy Prophet, after performing his Isha prayer went towards the graveyard of Baqee, called Abu Bakr, Umar and ‘Ali and told them: “Go towards the People of the Cave and convey to them my Salaam; and O Abu Bakr! you may salute them first as you are elder in age, then Umar, and next Uthman. If any of you gets a reply then he should convey to them my salaam. In case they do not respond to your salutation then O ‘Ali You should step forward and salute them.”
Then the holy Prophet ordered the breeze to raise all of them up and take them to the cave of People of the Cave. Another tradition says that the holy Prophet made them sit on a board and commanded it to carry them all to the cave. The, after reaching there, Abu Bakr stepped forward and said, Salaam, there was no response. Next Umar and Uthman too did the same but there was no reply. Finally Amir al-Mu’minin stepped forward and said, “Assalaamu alaikum wa rehmatullaah we beraakaatuhu O Residents of the Cave! You believed in your Creator. May Allah increase your guidance and keep your soul sound on faith. I am a courier of Allah’s last Messenger.”
Hearing the voices of the People of the Cave, they rose and they said, “Welcome! Long live the Prophet of Allah and his Legatee courier. O Wasi of the Prophet! may peace and blessing of Allah be upon you.” ‘Ali asked them, “How did you know that I am the Legatee of the last Prophet?” They said, “A kind of barrier has been put on our ears so that we may not be able to hear anyone’s voice nor will we be able to talk with anybody except a Prophet or a Legatee of a Prophet. O Legatee of the Prophet! How is the Prophet? How is his army” and they enquired very extensively about the holy Prophet and his events. Then they said, “Tell us also about your companions because we can talk only with a Prophet or his legatee (Wasi).” addressed his companions and asked: “Did you hear whatever the People of the Cave said?” They said, “Yes, we did.” Then ‘Ali said, “Be witness.” In short, all of them (thereafter) turned towards Madinah. The air then raised them up and carried them to the holy Prophet. They related to him whatever they had seen and heard. He also asked Abu Bakr, Umar and Uthman to be witness to what had happened. They said, “All right.” Then he told them emphatically to remember their witnessing well and went to his residence.
Reference: Hayat Al-Qulub, Vol. 1, Stories of the Prophets