IMĀM ASH-SHĀFI‘Ī NARRATES in al-Umm a hadith with an isnād that is mursal, according to which the Messenger of Allah 
said: “Seek acceptance of du‘ā’ when armies meet, when the iqāmah for ṣalāh has been called, and when rain falls.” Ash-Shāfi‘ī said: “I have memorised from more than one person [reports enjoining] the seeking of acceptance when rain falls and at the time of the iqāmah for ṣalāh.” [1].
said: “Seek acceptance of du‘ā’ when armies meet, when the iqāmah for ṣalāh has been called, and when rain falls.” Ash-Shāfi‘ī said: “I have memorised from more than one person [reports enjoining] the seeking of acceptance when rain falls and at the time of the iqāmah for ṣalāh.” [1].References
[1] Imam ash-Shāfi‘ī in Kitāb al-Umm (1/223–224). Ibn Ḥajar states that this is a good maqṭū‘ narration (i.e. attributed to one of the Tābi‘ūn, the generation after the Companions) which falls into the category of a mursal narration (i.e. lacking a Companion’s name in the chain of transmission).