Surah As-Saf — Ayah 3 (61:3)
كَبُرَ مَقۡتًا عِندَ ٱللَّهِ أَن تَقُولُواْ مَا لَا تَفۡعَلُونَ ٣
English translation (Saheeh International)
Greatly hateful in the sight of Allāh is that you say what you do not do.
Brief commentary
It is a most detested thing to Allah that you say what you do not do. It is only appropriate for a believer to be truthful with Allah, and for his actions to confirm his statements.