Derived patterns have characteristic maṣdars, while actual lexemes can show attested variation.
FormPast exampleMaṣdar example
Ifʿālأَكْرَمَإِكْرَامٌ
Tafʿīlعَلَّمَتَعْلِيمٌ
Tafaʿʿulتَعَلَّمَتَعَلُّمٌ
Mufāʿalahقَاتَلَمُقَاتَلَةٌ
Tafāʿulتَشَاتَمَتَشَاتُمٌ
Iftiʿālاِخْتَارَاِخْتِيَارٌ
Istifʿālاِسْتَعَانَاِسْتِعَانَةٌ
Infiʿālاِنْكَسَرَاِنْكِسَارٌ
The source also notes variations within Tafʿīl, such as تَسْلِيمٌ, تَجْرِبَةٌ and تَكْرَارٌ. Do not treat a typical pattern as an exceptionless lexical rule.