He said to them, "Go into all the world and preach the gospel to all creation. (Mark 16:15)

Though the above saying is a later addition and never was part of the original writing of "Mark", lets for argument sake accept it was written by him. Notice how "Jesus" said, "Go into all the world and preach the gospel to all creation. In other words, Christians are to preach the gospels only. Christian are no to use any other scriptures period. Jesus didn't say, "go debate them using their scriptures" rather " "Go into all the world and preach the gospel to all creation".

If this is the case, who then do Christians use Islamic sources when preaching with us? They should use the gospels only as instructed by their so called "saviour". There is no Christian on the planet who can preach to Muslim without mentioning about Islam, Quran, Hadith etc. when it's clearly written in black and white to preach the gospels only, not that you should make mention of their scriptures.

The Quran on the other hand, instructs us to "come to common terms" to "reason and argue". one way to reason and argue would be study and learn what your opponent is saying, providing you are learned in that field.

Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him) said:

It is permissible for the well versed scholar to read them in order to refute the opponents of Islam among the Jews and Christians, as the Prophet (blessings and peace of Allah be upon him) called for the Torah when the Jews denied the ruling of stoning, so that he could look at it, and after that they admitted it.

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said:
As for the seeker of knowledge who has sufficient knowledge that enables him to distinguish truth from falsehood, there is nothing wrong with him learning about them – namely the Gospels – in order to refute what they contain of falsehood and establish proof against their followers.

End quote from Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen (1/33)

However for Christians there is no such doctrine, where they are to study other faiths and use it when they are preaching their gospels. So next time stop quoting from our Scriptures and stick to your gospels only as instructed by your so called "saviour"

Lets see how you PREACH THE GOSPELS ONLY!