We know that we cannot call the present day non-Muslims as kafir since the truth of Islam is not presented to them the way it was done by prophet in the form of itmam e hujjat (conveying the truth conclusively). My question is how did the companions of the Prophet (sws) refer to the people when they conquered far and wide beyond Arabia. Since those people (common civilians) did not witness itmam e hujjat they could be called as kafir. Did the companions (sahaba) also call the kafir or non Muslim or something else? Is there any authentic record where we see the Companions (sahaba) making distinction between kafir and non Muslim? My friend says there is an ijmah on calling non-Muslims as kafir through out 14 centuries. Only in the last decade people started not using kafir for non Muslims.
We can call the present day non-Muslims as kafirs if we take into consideration the fact that the Qur'an has used the word kafir in two senses.
1. People who have denied the truth regardless of the fact that this denial is deliberate or because of some other reason (example of this usage can be seen in the opening verses of Surah Qaf).
2. People who have denied the truth deliberately and have thereby come worthy of God's punishment and condemnation (example of this usage can be seen in Surah Kafirun).
It is when used in the latter sense that the Qur'an gives many directives of punishment for them. When used in this sense the alif lam of 'had (alif lam of specification) appended to the word kafir points to this specific category of non-Muslims. It is such non-Muslims against whom Muslims were required to sever ties of friendship and not mutually receive inheritance or asked to wage war against. This category of non-Muslims comes into being in the time of the Messengers of God since only in their times their deliberate denial can be ascertained through God.
If today we call non-Muslims as kafirs then it has to be in the first sense since we can never know after the termination of the institution of wahi whether this denial is deliberate or due to some other reason. In other words, if use the word kafir for them today then we must realize that this does not refer to the condemned kafirs; it only means the kafirs who have rejected Islam for any reason.
As far as the kafirs of the time of the Companions were concerned against whom they waged war against, they belonged to the second category. True they did not witness the itmam ul hujjah of the Prophet; however, they witnessed the result of the itmam ul hujjah in Arabia. About whose initiation in Arabia they had been informed through the epistles of the Prophet. Coming about of itmam ul hujjah in itself becomes an itmam ul hujjah for the onlookers. When sun comes out you do not need to substantiate its appearance through reasoning. It is a witness on its own existence.
Thus when the sahabah attacked the adjacent territories, news of the beginning of itmam ul hujjah on Arabia had already been communicated to the rulers of the countries through letters of the prophet. As far as the masses were concerned they were to be spared the fate of being attacked if they had questions or wanted clarification as was the case of the polytheists (mushrikeen) in the time of the Prophet.