In a witness testimony at the FBI, it shows that Al-Qaeda received terrorist training from Iran and its proxy Hezballah
As was revealed at the trial that took place in New York earlier this year, a former member of Bin Laden's Al-Qaeda network began working with the United States government in 1996. That witness revealed that Bin Laden had a terrorist group, Al-Qaeda, which had privately declared war on America and was operating both on its own and as an umbrella for other terrorist groups. The witness revealed that Al-Qaeda had a close working relationship with the aforementioned Egyptian terrorist group known as Egyptian Islamic Jihad. The witness recounted that Bin Laden and Al-Qaeda were seeking to obtain nuclear and chemical weapons and that the organization engaged in sophisticated training. He also revealed that Al-Qaeda obtained specialized terrorist training from and worked with Iranian government officials and the terrorist group Hezballah.Source: FBI Testimony
Some say that this is hard to believe since Shiites like Iran and Al-Qaeda which are Sunnis cannot get along. But Sudan's Islamist leader, Turabi convinced them to leave their differences aside for a greater cause like global jihad.
Bin Ladin seemed willing to include in the confederation terrorists from almost every corner of the Muslim world. His vision mirrored that of Sudan's Islamist leader, Turabi, who convened a series of meetings under the label Popular Arab and Islamic Conference around the time of Bin Ladin's arrival in that country. Delegations of violent Islamist extremists came from all the groups represented in Bin Ladin's Islamic Army Shura. Representatives also came from organizations such as the Palestine Liberation Organization, Hamas, and Hezbollah.Source: The 9/11 Commission Report
Turabi sought to persuade Shiites and Sunnis to put aside their divisions and join against the common enemy. In late 1991 or 1992, discussions in Sudan between al Qaeda and Iranian operatives led to an informal agreement to cooperate in providing support-even if only training-for actions carried out primarily against Israel and the United States. Not long afterward, senior al Qaeda operatives and trainers traveled to Iran to receive training in explosives. In the fall of 1993, another such delegation went to the Bekaa Valley in Lebanon for further training in explosives as well as in intelligence and security. Bin Ladin reportedly showed particular interest in learning how to use truck bombs such as the one that had killed 241 U.S. Marines in Lebanon in 1983.The relationship between al Qaeda and Iran demonstrated that Sunni-Shia divisions did not necessarily pose an insurmountable barrier to cooperation in terrorist operations. As will be described in chapter 7, al Qaeda contacts with Iran continued in ensuing years.