In the late 1990s, Al-Timimi cofounded an Islamic center in Falls Church, Virginia with his mentor, Sheikh Jafar, which they named Dar al-Arqam. Al-Timimi became its primary lecturer, and delivered weekly lessons on Salafiya to approximately a hundred attendees a week. According to Umar Lee, Al-Timimi's lectures "became 'the place to be' for the youth of the masjids throughout the D.C. area," who were attracted to the fact that "this was a man who was born and raised in America, spoke in clear English, and not only had a great knowledge of the "dīn" (religion) but was college educated, a cancer researcher, and a very serious intellectual. This was a man who could take the knowledge of the Salaf and make it applicable to your everyday life and could speak in a language we all understood."