Hot answers tagged tying-knots-kosheir
The book The 39 Avoth Melacha of Shabbath* has an illustration that specifically forbids this (as Rabbinic, IIRC). If you have a copy, it sources every statement. * Yes, it is targeted at children, it is still well sourced, even if it only picks one opinion to go with (generally the Mishna Brura) and eschews ambiguity.
If the knot is high up to the top and if it is about to be undone you can bring down lower but do not tighten it. Shulchan aruch harav hilchos tzizis
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