Let's post ahadith and examples of duas' in this thread which were answered straightaway, as a proof of Allah.
Sahih Al Bukhari Volume 2, Book 17 [istisqa/seeking rain], Number 126:
Narrated Sharik bin 'Abdullah bin Abi Namir:
I heard Anas bin Malik saying, "On a Friday a person entered the main Mosque through the gate facing the pulpit while Allah's Apostle was delivering the Khutba. The man stood in front of Allah's Apostle and said, 'O Allah's Prophet! The livestock are dying and the roads are cut off; so please pray to Allah for rain.' "
Anas added, "Allah's Prophet (p.b.u.h) raised both his hands and said, 'O Allah! Bless us with rain! O Allah! Bless us with rain! O Allah! Bless us with rain!' "
Anas added, "By Allah, we could not see any trace of cloud in the sky and there was no building or a house between us and (the mountains of) Sila." Anas added, "A heavy cloud like a shield appeared from behind it (i.e. Sila' Mountain). When it came in the middle of the sky, it spread and then rained." Anas further said, "By Allah! We could not see the sun for a week.
Next Friday a person entered through the same gate and at that time Allah's Prophet was delivering the Friday's Khutba. The man stood in front of him and said, 'O Allah's Prophet! The livestock are dying and the roads are cut off, please pray to Allah to with-hold rain.' " Anas added, "Allah's Prophet raised both his hands and said, 'O Allah! Round about us and not on us. O Allah! On the plateaus, on the mountains, on the hills, in the valleys and on the places where trees grow.' So the rain stopped and we came out walking in the sun." Sharik asked Anas whether it was the same person who had asked for the rain (the last Friday). Anas replied that he did not know.
There's much more examples similar to this. Keep in mind this was the Arabian Peninsula where it hardly rained at all.
This is a statement coming from a man who could never lie about Prophet Muhammad, because lying about God's Messenger - whether 'good' or bad - is threatened with the hellfire. So even if someone had a good intent - they could not lie about him. So it is a sign that its a response from Allah straightaway.