What is the ruling on lengthening one fingernail while keeping the others short?

A Muslim should not leave their nails, or any part of them, long, as this goes against the Sunnah. Trimming nails is among the characteristics of the fitra (innate disposition) and the sunnahs of necessity. It is strongly disliked (makruh shaddid) to delay cutting them for more than forty days. It may even become forbidden (haram) if dirt accumulates under them, preventing water from reaching the skin during purification. There is no difference in this ruling between one nail or more, unless leaving a single nail long is an imitation of the immoral, in which case it becomes even worse.