SHAFAQNA (Shia International News Association) – Allah (SWT) told the Prophet Mosa (Moses; AS): Next time you come for prayers bring a person who in your opinion, you are better than him. The Prophet Mosa (AS) searched and found no one because he could not find the courage to say to those who pass by him, I am better than you are. So he decided to take an animal. He saw an ill dog and told himself, I will take this dog with me.
He put a lead on the dog and took it along with himself but after a while regretted and released the dog and came alone to pray to God. God asked Mosa (AS): Why you did not obey My order? Mosa (AS) replied: O’ my God, I could not find anyone who is lower than me. God said to Mosa (AS): I swear to My magnificence and greatness that if you could have considered a person to be lower than yourself, I would have removed you from the list of the prophets .
Source: The stories of the Prophets (Farsi version)