"The Most Merciful, so ask about Him one well-informed," meaning: one who is well-informed [about the servants].
Muhammad said: Whoever reads 'Ar-Rahman' in the nominative case (raf'), it is based on it being the subject (mubtada'), and the predicate is 'so ask about Him.'
﴿الرَّحْمَن فاسأل بِهِ خَبِيرا﴾ أَيْ: خَبِيرًا [بِالْعِبَادِ].
قَالَ مُحَمَّدٌ: من قَرَأَ (الرَّحْمَن) بِالرَّفْعِ فَعَلَى الِابْتِدَاءِ (وَالْخَبَرُ ﴿فَاسْأَلْ بِهِ﴾.
