Is the sermon for Salat al-Istisqa obligatory?
Chapter on the Prayer for Rain (Istisqa)
Al-Mughni
Book of the Eclipse Prayers (Solar and Lunar)
Primary text
Regardless of when the sermon is delivered, it is permissible to perform it or omit it, as the sermon is not obligatory according to all narrations. The preferable practice is one sermon delivered after the prayer, mirroring the Eid prayer, which allows for immediate relief (rain) if the supplication is answered before the necessity of praying in the rain arises.
Supporting text
The statement by Ibn Abbas that the Prophet did not deliver a sermon like 'your sermon' is interpreted as negating the specific description of the sermon, not the existence of the sermon itself; rather, the majority of his sermon was supplication, humility, glorification (takbir), and turning to change the direction of the cloak.