"The Messenger of Allah  (صلى الله عليه وآله وسلم) said:‘Verily Allah the Almighty has prescribed the obligatory deeds, so do not neglect them; He has set certain limits, so do not go beyond them; He has forbidden certain things, so do not indulge in them; and He has said nothing about certain things, as an act of mercy to you, not out of forgetfulness, so do not go enquiring into these.‘"

[It was narrated on the authority of Abi Tha'labah Al-Khushani Jurthum bin Nashir, radiyallahu 'anhu - Related by Al-Daraqutni and others - Al-Nawawi said this is a hasan (fine) hadith]

" إِنَّ اللهَ تَعَالَى فَرَضَ فَرَائِضَ فَلاَ تُضَيِّعُوهَا، وَحَدَّ حُدُوداً فَلاَ تَعْتَدُوهَا، وَحَرَّمَ أَشْيَاءَ فَلاَ تَنْتَهِكُوهَا، وَسَكَتَ عَنْ أَشْيَاءَ رَحْمَةً لَكُمْ غَيْرَ نِسْيَانٍ فَلاَ تَبْحَثُوا عَنْهَا"
[حَدِيثٌ حَسَنٌ رَوَاهُ الدَّارَقُطْنِي وَغَيْرُهُ]

Allah Most High says: "He who is hostile to a friend of Mine I declare war against. My slave approaches Me with nothing more beloved to Me than what I have made obligatory upon him, and My slave keeps drawing nearer to Me with voluntary works until I love him. And when I love him, I am his hearing with which he hears, his sight with which he sees, his hand with which he seizes, and his foot with which he walks. If he asks me, I will surely give to him, and if he seeks refuge in Me, I will surely protect him"

(Sahih Bukhari - Fath al-Bari, 11.340 41, hadith 6502) [src: suhba.org]