Abu Huraira reported: The Messenger of Allah, peace and blessings be upon him, said, “The servant is closest to his Lord during prostration, so increase your supplications therein.”
Source: Ṣaḥīḥ Muslim 482
Grade: Sahih (authentic) according to Muslim
عَنْ أَبِي هُرَيْرَةَ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ أَقْرَبُ مَا يَكُونُ الْعَبْدُ مِنْ رَبِّهِ وَهُوَ سَاجِدٌ فَأَكْثِرُوا الدُّعَاءَ
482 صحيح مسلم كتاب الصلاة باب ما يقال في الركوع والسجود