An Imam is a guide and one who is followed. The Prophets are also Imams as well as the Sahabah. However, the titles of Nabi and Rasool are more suitable and more honourable for the Prophets because these titles are specifically for them. As a result, it is impermissible to address one who is not a prophet with these titles. In the similar manner it is more respectful to address a Sahabi as Sahabi because this title is confined to them. To address a non-Sahabi by this title is not permissible. Besides the Imam of the Masjids, the title Imam is generally used to address a very learned scholar, who presents the laws and rules of Shari?ah in a regulated fashion, which is a means of direction for many people. People become affected by his competency and begin following him, thus making him their Imam. In this regard there are four famous Imams, Imam Abu Hanifah, Imam Shafi?ee?, Imam Malik and Imam Ahmed bin Hambal.
As a result one would not be violating the honour of any Sahabi by addressing a non-Sahabi as an Imam. It is quite clear that the meaning of Imam which is intended by the Shias is not the same as that of the Sunnis. In calling them Imams we would be imitating the Shias and therefore refrain from doing so.
and Allah Ta'ala Knows Best
Mufti Ahmad Suliman