Imam Ghazali (may Allah have mercy on him) narrates the saying of the blessed Prophet , صلى الله عليه وسلم
من ضيع سنتى حرمت عليه شفاعتى
Meaning that whoever abandons my way of doing things (sunna) will make my endorsement (i.e. shafaet on the Day of Judgement) impossible for him/herself.
Makashafat al-Quloob, page 74 /internet edition
May Allah give us the tawfiq and firm determination to follow Sunna. Amin