Hakim al-Umma Shaykh Ashraf Ali Thanawi (Allah have mercy on him) said,

 ‘Attributing a statement or an action to any individual, especially a believer (momin) without an explicit proof as per the ruling of Shariah is the clear sin of false allegation (buhtan) . This is especially so if this is in relation to a an esoteric issue, like intention (niyyah), etc.’

Risala shiq al-gain an Ali wa Hussain (Allah be pleased with them), page 8