Is it a condition that the person leading the prayer must have attended the sermon?
General Chapter
Al-Mughni
Book of Friday Prayer
Primary text
There are two narrations concerning this requirement. One view holds that attendance at the sermon is required. This is the opinion of Sufyan al-Thawri, the companions of Abu Hanifa (Ashaab al-Ra'y), and Abu Thawr. The reasoning is that since the leader in Jumu'ah is an Imam for Jumu'ah, attending the sermon is a prerequisite, similar to when no substitution has been permitted.
Supporting text
The second view is that attendance is not required. This is the position of al-Awza'i and al-Shafi'i. The rationale is that since the substitute is qualified to lead the Jumu'ah prayer in the first place, their leading it is valid, even if they missed the sermon, similar to a situation where they attended the sermon.