السلام عليكم ورحمة الله وبركاته This dua: اللَّهُمَّ أَعِنِّي عَلَى ذِكْرِكَ، وَشُكْرِكَ، وَحُسْنِ عِبَادَتِكَ Is after every prayer or only Fard and how do we know if it's 3am or khas. I heard someone saying this is related to usul fiqh

Ustadh AbdulAziz al-Haqqan

This is before u say tasleem from any salah, as for usool al fiqh then attend alwaraqat that we have explained here.