«وَلَا أُصَفِّي نَيْلِي لِمَنْ يَتَمَنَّى مَنِيَّتِي»
I do not reserve my purest benefaction for someone who wishes me dead.
Nayl refers to something received or given as a benefit; maniyyah means death. The near sounds make the line memorable, while the concepts—doing good and wishing harm—conflict sharply.
The contrast adds intention to the speaker's criteria for trust. Against the previous man's unrestricted goodwill, he professes to consider both another person's motives and conduct.