Al-Imām ibn Bāz [may Allāh have mercy on him] said:
“A sin committed in the ten days of Dhul-Hijjah is graver and worse [in punishment] than a sin committed in [the month of] Rajab, Sha’bān [and other months].”
Majmū Fatāwa 9/389 | Ash-Shaykh ibn Bāz [may Allāh have mercy on him]