There r many short incedents told abt Nalwa, donno if true.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/history-of-sikhism/175-sardar-hari-singh-nalwa.html
One is abt him in peshawar, he along with some 20-30 singhs were attacked by 200 pathans. Being short in number, the sikhs took shelter in a nearby haveli. They asked for the peace terms but the pathans were for Nalwa. At night it rained a lot. In the early morning, the singhs saw local ppl hemmering their mud roofs. When he asked, someone told that the local mitti was called "kuttan mitti" bcoz whenever it rained, they had to do this exercise otherwise it leaked. So Nalwa said that those pathans were made of the same Mitti.... so the only way to keep them under control is to hammer them regularly. So all of them attacked the pathans with full vigour and after some time all of them were asking peace from the Sikhs.
Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=175
The other story is when he was in Jamraud, a local girl "bano" came to him asked him to fulfill her wish. She wanted to have a son like Nalwa. She asked him to marry her. But Nalwa being married once, refused to do so. So she argued that she had heard no one ever went empty handed from the darbar of Guru Nanak. So why she was being refused like this. Then Nalwa called her back, touched her feet and said "I present myselt to u as ur Son"