In the Book of Numbers we read about Moses and the seventy elders of Israel gathering before the LORD, all of whom prophesied as a result of the Spirit:
Numbers 11:24-26: "So Moses went out and told the people the words of the LORD. Also, he gathered seventy men of the elders of the people, and stationed them around the tent. Then the LORD came down in the cloud and spoke to him; and He took of the Spirit who was upon him and placed Him upon the seventy elders. And when the Spirit rested upon them, they prophesied. But they did not do it again. But two men had remained in the camp; the name of one was Eldad and the name of the other Medad. And the Spirit rested upon them (now they were among those who had been registered, but had not gone out to the tent), and they prophesied in the camp*" (emphasis added).
Why do we not read of any admonition against Eldad and Medad, who stayed in the camp? Maybe we are to understand they were infirmed? Or was their presence perhaps optional?