The reliability of Allah's word (wa'd)

لَّهُمْ فِيهَا مَا يَشَآءُونَ خَـٰلِدِينَ ۚ كَانَ عَلَىٰ رَبِّكَ وَعْدًا مَّسْـُٔولًا

For them therein is whatever they wish, [while] abiding eternally. It is ever upon your Lord a promise [worthy to be] requested.