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
Hasan al-Basri (may Allah have mercy on him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever takes blood money and then kills, I will never pardon him."
This is munqati' (its chain is broken), and it has also been narrated with a connected chain.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16045
Jabir bin Abdullah (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) said: "I will not pardon one who kills after taking the blood money."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16046