"And when the seas are filled with flame," Al-Hasan said: meaning, they overflowed.
Muhammad said: The literal meaning of "are filled with flame" (sujjirat) is that they are filled, such that they overflow into one another and become a single entity; this is the meaning of Al-Hasan's statement.
﴿وَإِذا الْبحار سجرت﴾ قَالَ الْحَسَنُ: يَعْنِي: فَاضَتْ.
قَالَ مُحَمَّدٌ: سُجِّرت حَقِيقَتُهُ: مُلِئَت، فَيُفْضِي بَعْضُهَا إِلَى بَعْضٍ فَتَصِيرُ شَيْئًا وَاحِدًا؛ وَهُوَ مَعْنَى قَوْلِ الْحَسَنِ.