Is it permissible to give a colleague a portion of a 50 Riyal sum, received for performing a specific task in which the colleague did not participate, and is the colleague entitled to claim any of this sum?

If the relationship between you is a business partnership (partnership of bodies/labor), then the earnings are shared between you, even if one of you works without the other, unless the cessation of work was due to an unjustified refusal. If one of the partners stops working without a valid excuse, some scholars have held that he is not entitled to any part of the earnings that the other partner acquired alone. However, if the relationship is merely friendship or neighborliness, your colleague has no right to demand anything from you from the mentioned work's wage. If you wish to give him something out of affection or charity, then that is good.