“Mursal” is a term which is used when a Tabai’i (Those who have seen Sahaba/Companions of Holy Prophet) narrates from Holy Prophet directly, and they skip the Sahabi. That is,

‘

Tabai’i ->                      -> Holy Prophet

‘

Ibn Abi Hatim, famous Scholar of Ahlu Sunnah, has written a book named, al-Maraseel (plural of Mursal). His father was Mohammad bin Idrees, Abu Hatim al Razi. Dhabi introduced them in this manner in his book, Sair A’laam Nabala

 الإمام , الحافظ , الناقد , شيخ المحدثين

Imam, Hafiz, Critic, Sheikh of Scholars of Hadeeth

‘

Ibn Abi Hatim quotes his father in al-Maraseel, p. 27, and writes

43 – الْحُسَينُ بْنُ عَلِيٍّ بْنِ أَبِي طَالِبٍ رَضِيَ اللَّهُ عَنْهُمَا
77 – سَمِعْتُ أَبِي يَقُولُ حُسَيْنُ بْنُ عَلِيٍّ بْنِ أَبِي طَالِبٍ رِضْوَانُ اللَّهِ عَلَيْهِمَا لَيْسَتْ لَهُ صُحْبَةٌ

Hussein Bin Ali bin Abi Talib

I heard my Father (that mean Abu Hatim) who said that Hussein bin Ali did not had companionship (of Holy Prophet)

‘

Interestingly,  Ibn Abi Hatim in his another famous book of Rijal, al-Jarh wa al Ta’deel, 3/55, writes

249 – الحسين بن علي بن أبي طالب أبو عبد الله عليه السلام له صحبة روى عنه ابنه علي بن الحسين وابنته فاطمة بنت الحسين سمعت أبي يقول ذلك.

al Hussein bin Ali bin Abu Talib, Abu Abdullah (A’le his Salam), He had companionship. Narrated from him his Son Ali bin Hussein, and daughter Fatima bint Hussein. I heard my father saying that