Allah, the Mighty and Majestic, says: "Then whoever transgresses after that will have a painful punishment." [Surah al-Baqarah: 178]
Mujahid (may Allah have mercy on him) said: "Whoever transgresses after taking the blood money will have a painful punishment."
And Ata (may Allah have mercy on him) said: "(That is,) if he kills after accepting the blood money."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / Q16045