Is the preacher's saying at the end of the sermon, "I have said what I have to say," rooted in Islam, and is there any Sharia-related concern in it?

There is no harm in the preacher concluding his speech with "I say this and I seek Allah's forgiveness" or "I say my words"; for it is a phrase transmitted from the Prophet, peace and blessings be upon him. Ibn Hibban narrated from Ibn Umar that the Prophet, peace and blessings be upon him, said in his sermon on the Day of the Conquest of Mecca: (I say this and I seek Allah's forgiveness for myself and for you). Shu'aib Al-Arna'oot and Al-Albani graded it as authentic. Thabit ibn Qais ibn Shammas also said it in the presence of the Prophet, peace and blessings be upon him, and it was narrated in the sermons of Abu Bakr, Umar, and Ali, may Allah be pleased with them, and some contemporary scholars have used it. As for the objection that the preacher has mentioned things that are not his own words, such as verses and hadiths, it is incorrect; because the intention is the sermon in general, including the preacher's words and his citations.