"A reminder, and We have never been unjust" (Al-Shu'ara: 209), meaning: We would not punish them except after the clear proof and the argument have been established.
Muhammad said: "A reminder" (dhikra) can be in the accusative case (nasb) or the nominative case (raf'). The accusative case is as a verbal noun (masdar) based on the meaning of "except that it had warners"; meaning: those who remind with a reminder. The nominative case is based on the meaning: our warning is a reminder; that is, a notification. It is said: "I reminded him" (dhakkartuhu) using the feminine alif as in dhikra, or as dhikran, tadhkiran, and tadhkirah.
﴿ذكرى وَمَا كُنَّا ظالمين﴾ أَيْ: مَا كُنَّا لِنُعَذِّبَهُمْ إِلَّا مِنْ بَعْدِ الْبَيِّنَةِ وَالْحُجَّةِ.
قَالَ مُحَمَّد: ﴿ذكرى﴾ قَدْ تَكُونُ نَصْبًا وَتَكُونُ رَفْعًا، فَالنَّصْبُ عَلَى الْمَصْدَرِ عَلَى مَعْنَى: ﴿إِلَّا لَهَا منذرون﴾؛ أَيْ: مُذَكِّرُونَ ذِكْرًا، وَالرَّفْعُ عَلَى مَعْنَى: إِنْذَارُنَا ذِكْرَى؛ أَيْ: تَذْكِرَةٌ؛ يُقَالُ: ذَكَّرْتُهُ ذِكْرَى بِأَلِفِ التَّأْنِيثِ، وذكرا وتذكيرا وَتَذْكِرَة.