(Annoor) 24 : 7
وَالْخَامِسَةُ أَنَّ لَعْنَتَ اللَّهِ عَلَيْهِ إِنْ كَانَ مِنَ الْكَاذِبِينَ
And the fifth time he should testify that Let the curse of the Lord Allah be upon him if he is among the liars.
See explanation 3: 61; 5: 106-108 and 9: 119.