"While he was on the pulpit – the pulpit of Al-Basrah – ʿUtbah bin Ghazwain narrated that the Messenger of Allah ﷺ said: “Indeed a giant rock can be thrown from the brink of Hell and it will continue to fall into it for seventy years without reaching the bottom of it.”.He said: “ʿUmar used to say:'Increase in your remembrance of the Fire, for its heat is extreme, its bottom is distant, and its whips are of Iron.'” (Sahih)  

عَنِ النَّبِيِّ ﷺ قَالَ إِنَّ الصَّخْرَةَ الْعَظِيمَةَ لَتُلْقَى مِنْ شَفِيرِ جَهَنَّمَ فَتَهْوِي فِيهَا سَبْعِينَ عَامًا وَمَا تُفْضِي إِلَى قَرَارِهَا قَالَ وَكَانَ عُمَرُ يَقُولُ أَكْثِرُوا ذِكْرَ النَّارِ فَإِنَّ حَرَّهَا شَدِيدٌ وَإِنَّ قَعْرَهَا بَعِيدٌ وَإِنَّ مَقَامِعَهَا حَدِيدٌ