Arabic text
عن أبي هريرة رضي الله عنه أن رسول الله صلى الله عليه وسلم قال: «أَقْرَبُ مَا يَكُونُ الْعَبْدُ مِنْ رَبِّهِ وَهُوَ سَاجِدٌ، فَأَكْثِرُوا الدُّعَاءَ».
Translation
Abu Hurayrah (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "The nearest a slave to his Lord is while he is prostrating, so increase supplication."
Explanation
The Prophet (may Allah's peace and blessings be upon him) pointed out that the closer a servant comes to his Lord is when he is prostrating, for he puts the highest and noblest part of his body on the ground in submission and humility to Allah Almighty. The Prophet (may Allah's peace and blessings be upon him) ordered us to increase supplication while prostrating. Thus, we become submissive to Allah both by words and action.
Source: HadeethEnc.com