“Prayer [du‘a] is a powerful proof of God Almighty’s existence. Thus, God Almighty states in one place:
وَاِذَا سَاَلَکَ عِبَادِیۡ عَنِّیۡ فَاِنِّیۡ قَرِیۡبٌ ؕ اُجِیۡبُ دَعۡوَۃَ الدَّاعِ اِذَا دَعَانِ
“[And when My servants ask thee about Me, say: I am near. I answer the prayer of the supplicant when he prays to Me. (Surah al-Baqarah, Ch. 2: V. 187)]
“In other words, ‘When My servants ask you where God is and what is the proof of His [existence], say that He is very near, and its proof is that ‘I answer the prayer of the supplicant when he prays to Me.’ This answer is sometimes found through righteous visions and sometimes through divine revelations and inspirations. Furthermore, through prayers, the powers and might of God Almighty are manifested, demonstrating that He is All-Powerful and, as such, He resolves difficulties.”
(Al Hakam, 17 January 1905)