Reference: Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-‘Ilmiyyah wal-Iftaa., – Volume 2, Page 314, Question 3 of Fatwa No.8536
Question: What is the difference between the Muslims and the Ahmadiyyah (Qadianis)?
Response: The difference between the two is:
The Muslims are those who worship Allaah alone and follow His messenger Muhammad ﷺ and believe the he is the seal of [all] the prophets, and that there is no prophet [to come] after him.
As for the Ahmadiyyah who are followers of Mirza Ghulaam Ahmad, then they are disbelievers and not Muslims, because they claim that Mirza Ghulaam Ahmad is a prophet after Muhammad ﷺ, and whoever believes this ‘aqeedah then he is a disbeliever according to all the scholars of the Muslims, as Allaah (Subhaanahu wa Ta’aala) says:
{Muhammad is not the father of any man among you, but he is the Messenger of Allaah and the last [seal] of the Prophets}, [Soorah al-Ahzaab, Aayah 40].
And because of what has been authenticated on the authority of the Messenger of Allaah ﷺ that he said:
«I am the seal of [all] the prophets, there is no prophet after me», [Imaam Ahmad – volume 2, page 398 and 412, volume 3 page 79 and 248, volume 4, page 81, 84, 127 and 128, volume 5, page 278; al-Bukhaaree (Fat.h al-Baaree) number 3535; Muslim – number 2286 and 2287; Abu Daawood – number 4252].
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet ﷺ and his family and his companions.