Riyad as-Salihin, Book 9, Hadith 1099 (In-Book) ⓘ

'Abdullah bin Mughaffal (May Allah be pleased with him) reported: The Messenger of Allah said, "There is a Salat (prayer) between every Adhan and Iqamah; there is a Salat between every Adhan and Iqamah." (While saying the same for the) third time (he added), "It is for him who desires (to perform it)."[Al-Bukhari and Muslim].

وعن عبد الله بن مغفل، رضي الله عنه، قال‏:‏ قال رسول الله صلى الله عليه وسلم‏:‏ ‏"‏بين كل أذانين صلاة، بين كل أذانين صلاة، بين كل أذانين صلاة‏"‏ وقال في الثالثة‏:‏ ‏"‏لمن شاء‏"‏ ‏(‏‏(‏متفق عليه‏)‏‏)‏‏.‏