Is the Hadith true in which the Messenger of Allah wept out of longing for his beloved ones who believed in him but did not see him?

There is no hadith with this exact wording. However, it is narrated in Sahih Muslim that the Prophet, peace and blessings be upon him, said: "I wish I had seen our brothers." He then clarified that these are the ones from his Ummah who have not yet come, and that they will be recognized on the Day of Resurrection by their radiant faces and limbs due to the traces of ablution (wudu'). Imam Ahmad also narrated a hadith which states that the best people are those who come after the Companions, believe in the Prophet, peace and blessings be upon him, and have not seen him.