From an earlier answer of mine and be sure to read the follow-ups in the thread and the linked response from one of out all mighty moderators.

Most of these charges about a Nazi-Muslim Axis revolves around the figure of the grand mufti of Jerusalem, Amin al-Husseini. On the more extreme end of things, figures like Bibi Netanyahu and Sam Harris have elevated al-Husseini into a key decision maker within the Third Reich state apparatus.

The problem is that Al-Husseini's role in the Third Reich has been the subject of a good deal of politically-influenced embellishment where it becomes hard to disentangle myth from fact- /u/commiespaceinvader's has done an excellent job summarizing the Mufti's storied career in this answer.

For the most part, the historical record does not bear out Harris's picture of Palestinian history. Firstly, although al-Husseini was an important political figure in the interwar period, he was far from the only one and to call him the "leader of the Palestinians" is to impose a political unity that was not present in the Mandate. There were other Palestinian national leaders, but al-Husseini's activities in the Third Reich has led to him being elevated above others, some for legitimate scholarly reasons, others to delegitimize the Palestinian national movement (tellingly, the essay on Palestine in the anthology Arab Responses to Fascism and Nazism Attraction and Repulsion is entitled "More than the Mufti: Other Arab-Palestinian Voices on Nazi Germany, 1933–1945, and Their Postwar Narrations" underscores the outsized importance of al-Husseini and how some historians are tired of it).

The charge that al-Husseini visited Auschwitz largely comes from one source, Dieter Wisliceny, and the linked answer from out almighty moderator does show why Wisleceny is rather problematic source. Harris's invocation of Auschwitz is indicative of a wider problem when it comes to popular accounts (i.e. journalists, intellectuals, etc.) that examine al-Husseini. The Holocaust was an incredibly complicated process both in its genesis and execution. There is a marked tendency to assign blame in some way to al-Husseini for the Holocaust, whether through refusing to allow Jews access to Palestine or giving Hitler the idea for genocide. Sam Harris in particualr danced very closely to this line of argumentation, but the reality was al-Husseini was an incredibly marginal figure inside the Third Reich. Neither Himmler nor Hitler needed much prodding for genocide, especially from a non-European.

Finally, by not bringing out this wider context, Harris is presenting an incredibly skewed picture of al-Husseini's activities within occupied Europe. After the failure of the Iraq revolt in 1941, al-Husseini ended in Europe and worked for the German propaganda machine. But in doing so, he had to compete with other anti-British Arab emigres and navigate the various factions within the German state apparatus. Al-Husseini's anti-Jewish sentiments put him in ideological resonance with the SS, but in light of other emigre competitors like Rashid Ali al-Gaylani, making an alliance with this particular power bloc had a certain political logic behind it. Al-Gaylani's more secular and pan-Arabist politics had found support both in the Italian and German Foreign Ministries and he was in many ways a more "current" leader against the British, having participated in the Iraqi revolt in 1941. Al-Husseini's main stand against the British had occurred a generation earlier in 1929. Making the most of his connections to Himmler was a way for al-Husseini to gain the paltry resources the Axis devoted to the Arab cause away from an emerging rival.

The above does not to excuse nor does it mitigate al-Husseini's wartime activities. Now al-Husseini very much fits into the mold of being a bad man and a fool, but looking beyond his propaganda broadcasts there was a discernible desperation in his activities for the Third Reich to recognize the cause of Arab independence and place him at the head of it. This was a step that Hitler was unwilling to make. He helped in the recruitment of Bosnian Muslims in the SS Handschar Division, but he was often quite frustrated that the Germans did not put much weight behind his efforts and the Handschar was not used to fight for Arab independence. The Handschar's activities were localized in Bosnia and although it was involved in war crimes and other massacres, its relationship with the larger German military establishment was strained and largely a failure.

So while al-Husseini's activities in 1929 and the mid-30s put him at the starting point for Palestinian national activism, when you remove the moral revulsion from his wartime activities in Germany, al-Husseini emerges as a rather pathetic figure. As an exile, he found himself having to gain the favor of two states whose leaders who at best only supported his cause for tactical reasons. Neither Mussolini nor Hitler saw much use for the Arab world beyond the immediate tactical use of Arab nationalism to disrupt the British. By hitching his star to what was soon apparent to be a losing power in occupied Europe, al-Husseini was out of circulation with the wider developments within the Arab world. Al-Husseini had to reconstruct his network of political contacts after the war as well as deflect charges he was a German collaborator. So in short, al-Husseini's dalliances with National Socialism was more damaging to his political career and although he may have aspired to be "a full-blown collaborator", his would-be allies in Italy and Germany were mostly indifferent to him.