Narrated Anas: The Prophet (peace be upon him) was not accustomed to raise his hands in any supplication he made except when praying for rain. He would then raise them high enough so much so that the whiteness of his armpits was visible.
The Prophet's practice of raising his hands high enough so much so that the whiteness of his armpits was visible serves as a reminder to us to put forth our utmost effort in supplicating to Allah and seeking His help with sincerity and humility. It teaches us the importance of having faith in Him even during difficult times, knowing that He will provide whatever is best for us according to His wisdom and knowledge.