What is the ruling on the wedding contract handkerchief (mandīl kitāb al-kitāb) on which the names of the spouses and the date of marriage are written, and is it permissible to gift or buy it?

If the action is accompanied by the belief that it affects the marriage contract or that it is legislatively required, then it is a forbidden innovation (bid'ah), based on the Prophet's (peace be upon him) saying: "Whoever introduces into this matter of ours that which is not of it, it is rejected." If it is accompanied by a special belief, such as the marriage lasting as long as the handkerchief remains, then it is following harmful superstitions that detract from faith and intellect, because reliance on causes other than those that are legislatively or divinely beneficial is a deficiency in monotheism (Tawhid (definition)) and intellect. However, if it is merely a custom not accompanied by any specific belief, then it is among the permissible customs. Nevertheless, it is advised to abandon it to prevent the pathway to corrupt beliefs and the occurrence of ill omens or good omens associated with it.