The original injeel

Q: When the word "Injeel (Gospel)" was used in the Quran, is it referring to the four gospels of the Christians? If yes, why is it stated in the 3rd Sunnah: "48. And He (Allâh) will teach him ['Iesa (Jesus)]the Book and Al-Hikmah (i.e. the Sunnah, the faultless speech of the Prophets, wisdom, etc.), (and) the Taurât(Torah) and the Injeel (Gospel)." when the gospels came to be written after the lifetime of Jesus? If no. Do have a copy of that Injeel?

A: First of all, it is not the 3rd Sunnah. You are referring to Chapter 3 Verse 48 of the Holy Quran.What Allah is saying here is that He will teach Jesus the message of theTaurat (the Book that was revealed to Prophet Moses), and reveal the Injeel to Prophet Jesus. That what we have today as the New Testament is a collection of the Gospels written by people based on their memory of the teachings of Prophet Jesus. The teachings of Prophet Jesus are what we understand to be the "injeel".
Injeel refers to the revelations made to Prophet Jesus (Isa) by Allah. The New Testament that we have today is not the original, exact and complete Injeel, but rather contains portions of it as it 'according to' the memory of Mark, Mathew, Luke, John, Barnabas, and so on. They do contain the teachings of Jesus, but as it is based on the memory of the scribes who compiled it, it obviously contains may errors, omissions, lapses, contradictions, etc which are but human errors. Same is with the Torah, and other sacred texts. The reason why The Holy Quran did not suffer such a fate is because it was memorized by multiple people, word by word, right from the days of Prophet Muhammad upto this day. That is why the message has stayed intact. I do not know if any copy of the original injeel, torah, or any other book has survived to this day.
Hadith is a different story. Hadith books were compiled approximately 300 years after the death of Prophet Muhammad. They are based on the memory of the people that these scribes went to in search of the sayings of the Prophet, which in turn, is based on the memory of those from whom they heard it, and so on. Hence, there are many mistakes and contradictions in this body of work, and as such, this 'writing of men' cannot be taken as anyauthority. We can study it as historical documents, but we need to be careful to always check if a hadith is compatible with what Allah says in the Quran, otherwise it is not acceptable, as Prophet Muhammad lived his life totally in accordance with the injunctions of the Holy Quran, and we cannot imagine him doing or saying anything contradictory to the Quran. I would sincerely advice you to first study the Quran on its own, and then, after you've completed reading it, to branch out into studying the Hadith, Sunnah, historical books, and other sources. The Holy Quran(in Arabic) is the only document that we can vouch for as being authentically from Allah Almighty himself. Best is to study it in Arabic so as to be able to grasp the depth of meaning of each word, but if that is not possible, the next best thing is to comparatively study translations by different people to understand the closest meanings to the original message.
May Allah bless you and guide you, and may you find the true path. Amen.