What is the meaning of the Prophetic statement that a boy is held in pledge (murtahan) for his 'aqīqah?
All praise is due to Allah, and may peace and blessings be upon our Master, the Messenger of Allah.
The first interpretation: That if the boy dies in infancy without an 'aqīqah having been performed on his behalf, he will not intercede for his parents on the Day of Resurrection. This is the position of Imam Aḥmad ibn Ḥanbal, and Imam al-Khaṭṭābī concurred with him, stating: "The finest of what has been said regarding this matter is the position adopted by Aḥmad ibn Ḥanbal." — [Fatḥ al-Bārī by Ibn Ḥajar,{Vol.9/P.594]
The second interpretation: That the child is likened to a pledged object (marhūn) — one from which full benefit and enjoyment cannot be derived until it is redeemed. A blessing is only made complete upon the one blessed when they fulfil the obligation of gratitude (shukr), and the prescribed expression of gratitude for this particular blessing is what the Prophet ﷺ established as Sunnah — namely, the slaughtering of the 'aqīqah on behalf of the newborn as an act of thankfulness to Allah the Almighty and as a supplication for the wellbeing and safety of the child. This is the position of Mullā 'Alī al-Qārī. See: [Mirqāt al-Mafātīḥ Sharḥ Mishkāt al-Maṣābīḥ, Vol.7/P.2688]
And Allah Almighty knows best.
What is the ruling on istinja' after urination, and is it done with water and soap or with water only?
Istinja' from urine and stool is obligatory. It is permissible to perform istinja' with water alone, or with toilet paper alone. The best way is with toilet paper then water. If one wishes to suffice with one of them, then water is better. And Allah the Almighty knows best.
Is it valid to perform Tarawih prayer at home?
It is Sunnah for a Muslim to perform Tarawih prayer in congregation at the mosque.
However, if a person sometimes prays it at home in congregation with their family for a valid reason, there is no harm in doing so.
For some time I have been searching for a guiding shaykh to teach me the spiritual path (*sulūk*) and the Islamic sciences, but I have not found one. What should I do?
All praise is due to Allah, and peace and blessings be upon our master, the Messenger of Allah.
There is abundant good in this Ummah, and the scholars who guide and nurture are never cut off. The student of knowledge should strive in seeking them out, ask diligently after them, and draw from their learning.
As for one who cannot find a guiding and nurturing shaykh, he should send abundant prayers and peace upon our master the Prophet (peace and blessings be upon him), while keeping constantly to dhikr and worship and abstaining from the forbidden. For that will bring him to his goal in traveling toward Allah the Exalted. Imam Muḥammad al-Sanūsī (may Allah have mercy on him) said: “I have seen it said by some of the imams of Sufism that whoever lacks shaykhs of spiritual training (shuyūkh al-tarbiyah) should increase his invocation of blessings upon the Prophet (peace and blessings be upon him), for by it he will reach his goal.”
The scholar Aḥmad Zarrūq al-Mālikī (may Allah have mercy on him) said in Qawāʿid al-Taṣawwuf (p. 86), rule no. 114: “Dhikr is the decree of sainthood (manshūr al-wilāyah). Whoever is given dhikr has been given the decree. Our shaykh Abū al-ʿAbbās al-Ḥaḍramī (may Allah be pleased with him) said: ‘Keep constantly to dhikr and abundant blessings upon the Messenger of Allah (peace and blessings be upon him), for it is a ladder, an ascent, and a path to Allah the Exalted when the seeker does not meet a guiding shaykh.’” And Allah Almighty knows best.