Who are the Companions of the Prophet?

Definition of “the Companion”:
 

al-Hafiz Ibnu Hajar رحمه الله said: “The most correct opinion which I have accepted is that a Companion is: the one who met the Prophet صلى الله عليه وسلم while believing in him, and had died upon Islam (as a Muslim). Included in this (definition) is: the one who had spent a long period of time in the company of the Prophet صلى الله عليه وسلم and also the one who had spent only a short instance; and the one who narrated from him صلى الله عليه وسلم and the one who did not; and the one who participated with him صلى الله عليه وسلم in military expeditions and the who did not; and the one who had seen him صلى الله عليه وسلم only once, even if he did not attend his gathering; and the one who was not able to see him because of an excuse, like a blind person.” [al-Isaabah Fi Tamyyiz al-Sahabah (1/4)]

Imam an-Nawawi رحمه الله said: “The correct position, which is that of the great majority, is that every Muslim who saw the Prophet صلى الله عليه وسلم even for an hour, then that person is from his Sahaabah.” [Syarh Sahih Muslim (16/85) of an-Nawawi]

Imam Ahmad رحمه الله said: “Every person who accompanied the Prophet صلى الله عليه وسلم whether for a year, a month, a day, an hour, or even just saw him - is from his Companions.” [al-Kifayah fi `Ilmir-Riwayah (p.99) of al-Khatib al-Baghdadi]

Imam al-Bukhari رحمه الله said: “He who accompanied the Prophet صلى الله عليه وسلم or saw him - from the Muslims - then he is from his Sahaabah.” [Fath ul-Bari (7/1)]