Circumstantial evidence

Claims of influence might have been ignored were it not for the apparent similarities in the writing of the two men which were frequently noted. In addition to similarities, and reports by Nietzsche's close friend that he felt an affinity for Stirner, there exist three other circumstantial details which perhaps deserve mention.
The first is that Richard Wagner, who is well known as an early influence on Nietzsche, might have been familiar with Stirner's ideas. August Röckel was known to have introduced Wagner to Mikhail Bakunin, the Russian anarchist, and all three men were involved in the Dresden insurrection in May 1849. Wagner met with Bakunin several times during this period. Wagner is also known to have read the work of the anarchist Proudhon. Stirner was often closely associated with anarchist thought. Several authors have suggested that Wagner knew of Stirner's work, and some have suggested that Stirner influenced him.
The second involves Hans von Bülow, Cosima Wagner's first husband, who was a great champion and interpreter of Wagner's music. Nietzsche apparently first met him in the early 1870s when Nietzsche was frequently a guest of the Wagners and was introduced to members of their circle. Bülow visited Basel on March 27 of 1872, where he and Nietzsche held long conversations. In June of that year Nietzsche dedicated to von Bülow his new musical composition Manfred-Meditation and sent him a copy of the score. Von Bülow replied on July 24 with strong criticism of the piece. Nietzsche appears to have accepted this criticism with grace. In any case he did not break off all contact with von Bülow as we know that Nietzsche sent him a complimentary copy of the first part of Zarathustra in late summer or early fall of 1883. Nietzsche also sent von Bülow a copy of Beyond Good and Evil when the printing was finished in the late summer of 1886. He also wrote to Bülow as late as the 4th of January 1889, during his mental illness. Hans von Bülow is known to have been a great admirer of Max Stirner, and is reported to have known him personally. In April 1892 Bülow closed his final performance with the Berlin Philharmonic with a speech "exalting" the ideas of Stirner. Together with John Henry Mackay, Stirner's biographer, he placed a memorial plaque at Stirner's last residence in Berlin.
The third is the fact that from the 1st to the 17th of October 1865 Nietzsche visited the house of his friend Hermann Mushacke in Berlin. Hermann's father was one Eduard Mushacke, who in the 1840s had been a "good friend" of Stirner's. Nietzsche apparently got on well with Eduard Mushacke. Writing to his mother from Leipzig a few days later, on the 22nd of October he reported, "The life in Berlin was exceptionally pleasant and enjoyable. The old Mushacke is the most lovable man I ever met. We are on first name terms." One study links this newly discovered biographical detail with an "initial crisis" Nietzsche experienced in 1865, as a result of exposure to Stirner's ideas, leading to his study of Schopenhauer.