Fasting: Ascribing something false to Allah the Exalted, the Most Noble Prophet (S), or the Infallible Imams (A)
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 1575
If a fasting person intentionally ascribes something false to Allah the Exalted, the Most Noble Prophet (Ṣ), or the Infallible Imams (ʿA) – whether he does this verbally, in writing, or by making a sign and suchlike – and even if he immediately says, ‘I have lied’ or he repents, then based on obligatory precaution, his fast is invalid. The same applies, based on recommended precaution, to ascribing something false to Her Eminence [Fāṭimah] al-Zahrāʾ (ʿA) and the other Prophets and their successors.
Ruling 1576
If someone wishes to report a narration about which he does not have any evidence as to its authenticity, and he does not know whether it is true or false, then based on obligatory precaution, he must report it in such a way that he does not directly attribute it to the Most Noble Prophet (Ṣ) or the Infallible Imams (ʿA).
Ruling 1577
If someone quotes something as the word of Allah the Exalted, the Most Noble Prophet (Ṣ), [or the Infallible Imams (ʿA)] with the belief that it is true, and afterwards he realises that it was false, his fast does not become invalid.
Ruling 1578
If someone ascribes to Allah the Exalted, the Most Noble Prophet (Ṣ), [or the Infallible Imams (ʿA)] something that he knows to be false, and afterwards he realises that what he said was true, and he knew that this act would invalidate his fast, he must, based on obligatory precaution, complete his fast and keep a qaḍāʾ fast as well.
Ruling 1579
If someone intentionally ascribes to Allah the Exalted, the Most Noble Prophet (Ṣ), or the Infallible Imams (ʿA) something that has been fabricated by some other person, then as an obligatory precaution, his fast becomes invalid. However, if he simply narrates from the person who fabricated the falsehood without knowing it to be false, there is no problem [and his fast is valid].
Ruling 1580
If a fasting person is asked whether the Most Noble Prophet (Ṣ) [or Allah the Exalted, or one of the Infallible Imams (ʿA)] said such and such thing and he intentionally replies ‘Yes’ when he should say ‘No’, or he intentionally replies ‘No’ when he should say ‘Yes’, then based on obligatory precaution, his fast becomes invalid.
Ruling 1581
If someone correctly quotes the words of Allah the Exalted, the Most Noble Prophet (Ṣ), [or the Infallible Imams (ʿA)] and then says, ‘I lied’, or if at night he ascribes something false to them and on the following day when he is fasting says, ‘What I said last night is true’, then based on obligatory precaution, his fast becomes invalid unless his intention is to explain the state of his information [i.e. he means to assert that it is true that he did actually say that last night, not that what he said is true].