One verse

Srimad Bhagavatam 3.25.21

3.25.21

तितिक्षव: कारुणिका: सुहृद: सर्वदेहिनाम् । अजातशत्रव: शान्ता: साधव: साधुभूषणा: ॥ २१ ॥

titiksavah karunikah suhrdah sarva-dehinam ajata-satravah santah sadhavah sadhu-bhusanah

titiksavah
tolerant
karunikah
merciful
suhrdah
friendly
sarva-dehinam
to all living entities
ajata-satravah
inimical to none
santah
peaceful
sadhavah
abiding by scriptures
sadhu-bhusanah
adorned with sublime characteristics.

The symptoms of a sadhu are that he is tolerant, merciful and friendly to all living entities. He has no enemies, he is peaceful, he abides by the scriptures, and all his characteristics are sublime.