Allamah Muhammad ibn Abdur Rahman Sakhaawi said in
“القول البديع في الصلاة على الحبيب الشفيع صلى الله عليه وسلم”:
[I] It is narrated from Anas رضي الله عنه and he elevated it to the Messenger ﷺ:
“He who sends one salaat upon me on the day of Jumuah, Allah and the Angels will send a hundred thousand (100,000) salaat upon him, and will write for him a hundred thousand (100,000) rewards, and will remove a hundred thousand (100,000) sins from him, and will elevate him a hundred thousand (100,000) stages in Jannah.”
I did not find its basis. I feel it is not authentic. Rather I am sure it is fabricated.
Allamah Sakhawi clearly states that this is a fabrication. Here we see that he firstly used the same words he used for the narration which mentioned: “Allah made Ibrahim his Khalil…” [Hadith C] This is why we concluded that Sakhawi is saying that if it is not fabrication, then it is extremely weak.