"O you who believe! Do your duty to Allah and fear Him. Seek the means of approach to Him, and strive hard in His Cause as much as you can. So that you may be successful."
[Surat Al-Mā'idah, Ayah 35]
Shaykh Abdur-Rahman bin Naasir as-Sa'dee (رحمه الله) mentioned in his tafseer: