Mustahab (Recommended)
Actions that are recommended but not obligatory, and that give extra reward.
Mustahab (Arabic: مستحب) means "recommended" or "desirable" and refers to actions that are recommended in Islamic law but not obligatory. Performing a mustahab action earns reward, but omitting it is not a sin. In the context of prayer, there are numerous mustahab actions that enrich and deepen the prayer.
Mustahab actions in connection with prayer include: adhan and iqamah (call to prayer), nawafil (voluntary prayers), qunut in the second rak'ah, Tasbihat al-Zahra after the prayer, recitation of Ayat al-Kursi and dhikr after the prayer, praying in a mosque, praying in congregation, and praying at the prayer's preferred time (waqt al-fadilah).
Imam al-Sadiq (peace be upon him) said: "Allah's servant draws nearest to Him through the obligatory actions. But then he draws nearer through nawafil (voluntary actions), until Allah loves him. And when Allah loves him, He becomes his hearing, sight, and hand" (Al-Kafi, vol. 2). This hadith qudsi (divine hadith) shows that mustahab actions are the path to Allah's special nearness.
In Shia fiqh, there are hundreds of mustahab actions related to prayer, dhikr, du'a, fasting, and other forms of worship. Mafatih al-Jinan by Shaykh Abbas al-Qummi is essentially a collection of mustahab actions organized by time and occasion. For the believer, mustahab actions are an opportunity to earn extra reward, strengthen one's connection to Allah, and enrich one's spiritual practice without the obligation that accompanies wajib actions.
Related terms
Bismillah (In the Name of Allah)
The formula "In the Name of Allah, the Most Gracious, the Most Merciful," which opens prayer and action.
Tasbihat al-Zahra (Fatimah's Tasbih)
A special dhikr consisting of 34+33+33 repetitions, taught by the Prophet to his daughter Fatimah.
Salat al-Istisqa (Rain Prayer)
A special congregational prayer performed to ask Allah for rain during drought.
Du'a Nudba (The Lamentation)
A supplication about the 12th Imam's return, recited on Fridays and festivals.
Fard (Obligatory)
The obligatory acts in Islam, including the five daily prayers.
Sujud al-Tilawah (Prostration of Recitation)
A prostration performed when reciting or hearing specific Quranic verses.