Nevertheless, it is essential that the dissenters understand that even those who permit acting upon a weak hadith in matters of virtue do not allow it unconditionally. Al-Hafiz Ibn Hajar writes in Tabyin al-ʿAjab, pp. 3–4:

“It is well known that scholars are lenient in citing reports dealing with virtuous deeds, even when those reports are weak, provided they are not fabricated. Yet one must also stipulate that the person who acts on such a report believes it to be weak, and that he does not publicize it; otherwise someone may practice an act on the basis of a feeble report and thereby introduce into the religion what is not part of it, or an uninformed observer may imagine that it is a sound sunnah. Abū Muḥammad Ibn ʿAbd al-Salām and others have stated this explicitly. A person must beware of falling under the Prophet’s warning: ‘Whoever relates from me a hadith while he thinks it is false is one of the two liars.’ How much worse, then, for the one who acts upon it! There is no distinction between applying a hadith in legal rulings and applying it in matters of virtue, for both constitute part of the Sharia.”

From this passage three important conditions emerge for the permissibility of acting on a weak report:

1. It must not be fabricated.
2. The person who practices it must know that it is weak.
3. He must not broadcast his practice of it.

Regrettably, many scholars—let alone ordinary people—neglect these conditions. They act on a hadith without knowing whether it is authentic or weak; if they do know it is weak, they remain unaware of the degree of weakness—whether it is slight or so severe that acting on it is forbidden. Then they publicize their practice as though the hadith were sound, and countless illegitimate devotional acts have thus spread among Muslims, distracting them from the authentic acts of worship that have come down through reliable chains of transmission.