Fortress of the Muslim (Hisn al-Muslim)
حصن المسلم
(129) Chapter: Seeking forgiveness and repentance
(129) الاستغفار والتوبة
Hisn al-Muslim 252 
-- Allah's Messenger (ﷺ) said: "The closest that the slave comes to his Lord is when he is prostrating, so invoke Allah much (in prostration)." Reference: Muslim 1/350.
.وَقَالَ صلى الله عليه وسلم: أَقْرَبُ مَا يَكُونُ الْعَبْدُ مِنْ رَبِّهِ وَهُوَ سَاجِدٌ فَأَكثِرُوا الدُّعَاءَ.
Reference : Hisn al-Muslim 252