The answer before Badr

The army that left Madinah had not set out to fight a battle. When it became clear that a Makkan force was coming, the situation had changed from what people had agreed to, and the Prophet ﷺ put it to them.

He asked for their view. He asked more than once.

The Muhajirun answered first, and answered well. But the Prophet ﷺ kept asking, and the Ansar understood what the repetition meant: he was waiting for them specifically.

There was a reason for that. The pledge the Ansar had given at Aqabah was to protect him in Madinah, as they would protect their own families. It said nothing about marching out of the city to meet an army in the open. On the letter of it, they could have stayed behind and been within their rights.

Sa'd ibn Mu'adh stood up and said so — that he understood the question was meant for them — and then answered it. Go where you intend. We are with you. If you crossed the sea and went into it, we would go in with you.

The reports say the Prophet ﷺ was gladdened by it and the army moved.

What makes this worth remembering is not the enthusiasm. It is that Sa'd named the loophole out loud before declining to use it. He did not pretend the pledge covered this. He said the pledge did not cover it, and that they were coming anyway.