Rule 7: When wāw or yāʾ follows the additional alif of the active-participle pattern, the weak radical is represented by hamzah.
Word / formMeaning / explanation
قَاوِلٌ → قَائِلٌone who says.
بَايِعٌ → بَائِعٌseller.
خَاوِفٌ → خَائِفٌone who fears.
The resulting hamzah is not a new radical of the lexical root. قَائِلٌ still belongs to ق و ل, and بَائِعٌ to ب ي ع.