Does the protrusion of the inner part of the penis soil clothes and invalidate ablution, especially when sweating?

The meaning of "bāṭin al-dhakar" (inner part of the penis) is not clear. However, if what is meant is its erection or its touching of clothes, then nothing results from that unless it is accompanied by the discharge of secretions. It is stated in al-Sharḥ al-Ṣaghīr ‘alā Mukhtaṣar Khalīl that mere pleasure from looking or thinking does not invalidate ablution, even if an erection occurs. And human sweat is pure.