وَإِنْ كُنْتُمْ فِي رَيْبٍ مِمَّا نَـزَّلْنَا عَلَى عَبْدِنَا فَأْتُوا بِسُورَةٍ مِنْ مِثْلِهِ وَادْعُوا شُهَدَاءَكُمْ مِنْ دُونِ اللَّهِ إِنْ كُنْتُمْ صَادِقِينَ(23)  فَإِنْ لَمْ تَفْعَلُوا وَلَنْ تَفْعَلُوا فَاتَّقُوا النَّارَ الَّتِي وَقُودُهَا النَّاسُ وَالْحِجَارَةُ أُعِدَّتْ لِلْكَافِرِينَ (24)
                                                                                          Al-Baqarah 23-24                       

[23] And if ye are in doubt as to what We have revealed from time to time to Our servant, then produce a Sura like thereunto; and call your witnesses or helpers (if there are any) besides Allah, if your (doubts) are true.

[24] But if ye cannot - and of a surety ye cannot - then fear the Fire whose fuel is men and stones which is prepared for those who reject Faith.
(Reference: www.al-islam.com)

أَفَلا يَتَدَبَّرُونَ الْقُرْآنَ وَلَوْ كَانَ مِنْ عِنْدِ غَيْرِ اللَّهِ لَوَجَدُوا فِيهِ اخْتِلافًا كَثِيرًا
                                                                                        (An-Nisaa #82)
 

[82] Do they not consider the Qur-an (with care)? Had it been from other than Allah, they would surely have found therein much discrepancy.

[83] When there comes to them some matter touching (public) safety or fear, they divulge it. If they had only referred it to the Messenger or to those charged with authority among them, the proper investigators would have tested it from them (direct). Were it not for the Grace and Mercy of Allah unto you, all but a few of you would have followed Satan.

[84] Then fight in Allah's cause - thou art held responsible only for thyself - and rouse the Believers. It may be that Allah will restrain the fury of the Unbelievers; for Allah is the strongest in might and in punishment.
(Reference: www.al-islam.com)
 

فَإِذَا قَضَيْتُمُ الصَّلاةَ فَاذْكُرُوا اللَّهَ قِيَامًا وَقُعُودًا وَعَلَى جُنُوبِكُمْ فَإِذَا اطْمَأْنَنْتُمْ فَأَقِيمُوا الصَّلاةَ إِنَّ الصَّلاةَ كَانَتْ عَلَى الْمُؤْمِنِينَ كِتَابًا مَوْقُوتًا
        (An-Nisaa #103)                                    

[103] When ye pass (congregational) prayers, celebrate Allah's praises, standing, sitting down, or lying down on your sides; but when ye are free from danger, set up regular prayers: for such prayers are enjoined on Believers at stated times.
(Reference: www.al-islam.com)