See Shmot: Beshalah: 14:15
Rashi cites a Midrash explaining why Hashem tells Moshe to stop praying. He offers two reasons.
A No time to lengthen prayer if people are suffering
B. Hashem is asking, "why Bother ME? It's in Your hands!"
This reminds me of a wise statement about Prayer and Action:
PRAY as if everything depends upon G-d,
ACT as if everything depends upon you!