Mankind is One Ummah
Allah says;
إِنَّ هَذِهِ أُمَّتُكُمْ أُمَّةً وَاحِدَةً
Truly, this, your Ummah is one,
Ibn Abbas, Mujahid, Sa`id bin Jubayr, Qatadah and Abdur-Rahman bin Zayd bin Aslam said,
"Your religion is one religion."
Al-Hasan Al-Basri said;
"In this Ayah, Allah explains to them what they should avoid and what they should do."
Then He said;
إِنَّ هَذِهِ أُمَّتُكُمْ أُمَّةً وَاحِدَةً
Truly, this, your Ummah is one religion,
"Meaning, your path is one path. Certainly this is your Shariah (Divine Law) which I have clearly explained you."
So Allah says;
وَأَنَا رَبُّكُمْ فَاعْبُدُونِ
and I am your Lord, therefore worship Me.
This is like the Ayah;
يأَيُّهَا الرُّسُلُ كُلُواْ مِنَ الطَّيِّبَـتِ وَاعْمَلُواْ صَـلِحاً
O (you) Messengers! Eat of the Tayyibat (good things) and do righteous deeds.) Until His saying,
وَأَنَاْ رَبُّكُمْ فَاتَّقُونِ
(And I am your Lord, so have Taqwa of Me). (23;51-52)
The Messenger of Allah said;
نَحْنُ مَعَاشِرَ الاَْنْبِيَاءِ أَوْلَادُ عَلَّتٍ دِينُنَا وَاحِد
We Prophets are brothers from different mothers and our religion is one.
What is meant here is that they all worshipped Allah Alone with no partner or associate, although the Laws of each Messenger may have differed, as Allah says;
لِكُلٍّ جَعَلْنَا مِنكُمْ شِرْعَةً وَمِنْهَـجاً
To each among you, We have prescribed a Law and a clear way. (5;48