What Other Source Of Information Except Quran Did Prophet Muhammad Had?
He used to receive revelation from God, not only in the form of the Quran but in other matters. He was constantly under the supervision and protection of God. If he misjudged something about religion, he was corrected. Some errors in judgment have been reported in Ahadith. But in religious matters, he was guided and protected. See the verses: عَالِمُ الْغَيْبِ فَلَا يُظْهِرُ عَلَىٰ غَيْبِهِ أَحَدًا ‎﴿٢٦﴾‏ إِلَّا مَنِ ارْتَضَىٰ مِن رَّسُولٍ فَإِنَّهُ يَسْلُكُ مِن بَيْنِ يَدَيْهِ وَمِنْ خَلْفِهِ رَصَدًا ‎﴿٢٧﴾‏ لِّيَعْلَمَ أَن قَدْ أَبْلَغُوا رِسَالَاتِ رَبِّهِمْ وَأَحَاطَ بِمَا لَدَيْهِمْ وَأَحْصَىٰ كُلَّ شَيْءٍ عَدَدًا [These are matters of the Unseen, and] only He knows this Unseen, and He also never reveals this Unseen to anyone. As for those whom He chooses as His messengers, they can say nothing of their own; He guards them from behind and from the front so that He may know whether they have delivered the messages of their Lord; and He surrounds whatever is around them and keeps count of all their things.