It is reported that Al-ʿAwwām b. Ḥawshab – Allāh have mercy on him – said:
Boasting that you did a sin (when you did not) is worse than committing the sin.
Al-Daynūrī, Al-Mujālasah wa Jawāhir Al-ʿIlm, article 3073.
Ibn Qutaybah, explaining what is meant by boasting here, said:
It is when a person says, ‘I fornicated’, when he did not, or to say, ‘I killed a man’, when he did not, boasting and showing off. This is worse upon a man than committing the sin because he did not avoid the sin except that he would have done it if able. He is therefore like the one who does it, by intention. He goes even further by removing the cover (of reputation) from himself, and by the depravity of his audacity to commit sin and his lack of concern.