One of the name of God is "Al-Wahid Al-Ahad"

His sacred Being is unique, with no organs or gradients. He is the One with no parallel; He is the One with no associate.

Prior to God nothing existed: what exists is His creation: فَهُوَ الْمُتَوَحِّدُ بِالأزَلِ وَالأبَدِ، وَمُتَفَرِّدٌ بِالْوَحْدَةِ وَالأحَدِيَةِ.

The words Ahad and Wahid are the derivatives of the word Wahdat meaning “One-ness.” All creation and creatures are just reflections of His existence and everybody fades away in Him: كُلُّ مَنْ عَلَيْهَا فَانٍ  [1] “Everyone on it (the earth) must pass away” كُلُّ شَيئٍ هالِكٌ إلاّ وَجْهَهُ [2] “Everything is perishable but He.”

If a person becomes famous among his associates and friends as a man of ethics and good works and if he becomes distinguished as a loyal and sincere and if his friends unanimously believe that he is a good one, then he has grasped the genuine content of the known “Ahad” and its adjective form Wahid:

صِبْغَةَ اللَّهِ وَمَنْ أَحْسَنُ مِنْ اللَّهِ صِبْغَةً  [3]

“Receive the baptism of Allah, and who is better than Allah in baptizing?” Monotheism, truth, faith, virtue, generosity are God’s colors, and what color is better than His color?

Imam Ali (a.s), in his honorable Kumail invocation asks God to offer him the trait of being unique among his relatives and associates in God’s worshipping:

وَاجْعَلْني مِنْ أحْسَنِ عَبِيدِكَ نَصِيباً عِنْدَكَ، وَأقْرَبِهِمْ مَنْزِلَةً مِنْكَ وَأخَصِّهِمْ زُلْفَةً لَدَيكَ.