Q182 :Some scholars are of the opinion that it is
sunnah to drink what is left over by another person in his glass. How
could this be explained in the light of the fact that certain diseases
can be transmitted this way?
A182 : It is certainly not a sunnah to drink what
someone else has left over in his glass. When we say that it is a
sunnah, it means that Islam renetmends it. To have such a
renetmendation, we need to have some sort of instructions by the
Prophet. There is none in this particular case. But we have to
understand that in such a situation it is not sufficient that the
Prophet had shared the same glass or cup with other people. In order to
make sure that we know what he has renetmended, he would have followed
that with a verbal statement of some sort. The absence of any, means
that it is not a sunnah. It is true that we have some reports which
tell us that the Prophet was offered some drink when there were so many
people. There was little amount of that drink in the container. The
Prophet drank from it and passed it over to the person sitting next to
him. He drank his fill and passed it over again. The same was repeated
over and over again until everyone drank as much as he wanted. But that
was a special case and one of many incidents in the life of the Prophet
which Allah facilitated in order to reassure those early Muslims that
they were following the true religion taught by the Messenger of Allah
who always spoke the truth. As you say, certain diseases could be
transmitted through such a practice, which means, by necessity, that it
could not be renetmended by Islam.
Our Dialogue ( Source : Arab News – Jeddah )