Question: Some people pray for years and even perform pilgrimage, yet they do not pay khums. Is it obligatory on them to repeat their prayers and pilgrimage?

Answer: Based on precaution, it is obligatory on them to repeat prayers and pilgrimage, if the particular dress that they used in prayers, in tawaf and in salat of tawaf was from items on which khums had become due.
However, if only the dress they used in salat of tawaf was from items on which khums had become due, and they were ignorant (even out of negligence) of the law or the status of the dress, their pilgrimage is valid, but they have to repeat salat of tawaf if they had no excuse for their ignorance. [In this case,] they have, as a matter of precaution to return to Mecca [to perform the salat of tawaf again], if it does not entail great difficulty; otherwise they can perform that salat wherever they are.
Similarly, they will have to do the pilgrimage again if the animal offered as a sacrifice was bought with money on which khums had become due. However, if they had bought it with money whose unspecific portion was liable for khums -as is the case normally - there is no problem in their pilgrimage, even if they used it from the money on which khums had become liable; of course, they will be responsible for that amount [for payment of khums].
All this is applicable, if they knew about the obligation of khums and the law forbidding them to utilize items on which khums has become wajib or if they were ignorant out of negligence. But, if they were ignorant out of innocence, their prayers and pilgrimage are valid.

Ref: Ayatollah-al-Uzma Sayyid Ali al-Husayni al-Sistani
Link: Q & A Namaz - 2

Question: In an Indian village, the distance between two mosques is about one and a half Par sang (Farsakh) and since 1390 AH Friday prayer is recited in both.

Answer: It should be more than three miles between two places in where Friday prayer is recited. If it is less and both Imams start to say prayer simultaneously, both prayers will become null and vain. But if one of them starts sooner, his prayer is true and the second one is vain. As we know Friday prayer is not an obligatory in Imam Mahdi's absence, so leaving it to make the terms as true as possible won't cause suspicions. In addition Friday prayer should be recited by an innocent Imam or with the permission of them and in his absence we are not sure of its legality. Therefore you should say your noon prayer too for the sake of precaution, although you say Friday prayer.

Ref: Ayatollah-al-Uzma Seyed Mohammad Sadegh Rohani
Link: Fatwa's subject: Prayer- ID:49

Question: Honourable Sir, Assalaam-u-Aliakum Is Ali-un-Waliullah permissible to be recited in the Tashahud ? Does reciting it make the prayer batil ? wa salaam

Answer: If the word Ashhad is not recited-Ashhado anna Ali-un-Waliullah -the prayer is correct but for Izan (the call to pray) and Ighamah it is recommended.

Ref: Ayatollah-al-Uzma Seyed Mohammad Sadegh Rohani
Link: Fatwa's subject: Prayer- ID:71

Question: Is'ali-un-waliullah' wajib in 2zan/aqama & tashahud?

Answer: Saying it, is not obligatory in Azan but recommended.But it is not obligatory in Tashahod and even if it is counted as a part of prayer , it is not permissible to say it.

Ref: Ayatollah-al-Uzma Seyed Mohammad Sadegh Rohani
Link: Fatwa's subject: Prayer- ID:139

Question:
Wilayat al-Faqih:
1) Who is the Wilayat al-Faqih in these days?
2) Is it obligatory to do taqleed of the Wali al-Faqih?
3) If someone does taqleed of a marja other than the wali al-faqih and in a particular issue the fatwas of both differ, what is the duty of the moqallid? Can he follow his marja, or does he have to follow the Wilayat al-Faqih?

Answer: Wilayat al faqih is a branch issue that religious jurists did not agree on.The individual had to choose the most knowledgeable jurist that is described with all necessary conditions for imitation - Taqleed.
If determining the right religious jurist (Merji) was based on religious evidence then the individual should follow the verdicts of the chosen jurist whether this jurist believes in the issue of wilayat al faqih or does not.

Ref: Ayatollah-al-Uzma Sayyid Muhammad Sa'id al-Tabataba'i al-Hakeem
Link: Questions & Answers: Wilayat AlFaqih: Q1