Tafsir of Al-Qamar 54:12

وفجرنا اﻻرض عيونا

And We caused springs to gush forth from the earth. means, from every part of the earth, and even ovens in which fire was burning -- water and springs gushed forth,

فالتقى الماء

So, the waters met, means, of the heaven and the earth,

على أمر قد قدر

for a matter predestined. Ibn Jurayj reported from Ibn Abbas:

ففتحنا أبواب السماء بماء منهمر

(So, We opened the gates of the heaven with water Munhamir), "Torrential rain, the only water that fell from the sky before that day and ever since was from clouds. But the sky's gates were opened on them that day, and therefore, the water that came down was not from clouds. So both the waters (of the earth and the heaven) met according to a matter ordained.'' Allah said,

وحملناه على ذات ألواح ودسر