It is narrated from Sayyiduna Zaid bin Khalid Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Whoever touches his private part should perform ablution.
It is narrated from Sayyiduna Abdullah bin Amr bin al-As (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Whoever touches his private part should perform ablution, and likewise, any woman who touches her private part should also perform ablution.
It is narrated from Sayyiduna Abu Hurairah (may Allah be pleased with him) that the Noble Prophet (peace and blessings be upon him and his family) said: Whoever touches his private part with his hand, while there is no covering in front of him, then indeed, ablution becomes obligatory upon him.