This is a very detailed aspect of Tawassul and often the most misused. It involves asking another person to make dua on your behalf in the chance that it will increase the likelihood of your dua being
It is allowed to make tawassul by asking a living person to make Dua on your behalf, if you feel that such a person is a truthful, righteous person. So it is permissible to go to a scholar and ask him to make Dua for something that you want.
Safwan ibn Abdillah narrated: ‘I went to Syria, and visited Abu al-Darda in his home, but he was not present when I arrived. Umm al-Darda asked me, ‘Are you going to perform Hajj this year?’ I replied that I was, so she said: ‘In that case, do not forget to pray to Allah for us for good, for the Prophet [May the Peace and Blessings of Allah be upon him] used to say: “The dua of a Muslim for his brother in his absence is responded to. In his presence there is an angel that has been assigned to him; every time he makes a dua for his brother with good, the angel assigned to him says, Ameen, and to you the same. [Reported by Muslim, Ibn Majah, and Ahmad, from Abu al-Darda, as mentioned in Sahih al-Jami #3380.
Jabir ibn Abdillah reported that a woman came to the Prophet (May the Peace and Blessings of Allah be upon him) and said: “Pray for me and my husband”. So the Prophet responded: “May Allah have mercy on you and your husband” [Abu Dawud #1530]
When performing this tawassul it is better to not ask for personal duas, but rather a general dua. This principle is shown in the following narration: ‘Once, during the caliphate of Umar ibn al-Khattab, there was a severe drought that afflicted Madinah. The Muslims, under the leadership of Umar, went outside the city to perform salat-al-istisqa, the prayer for rain. After finishing the prayer, Umar said: “O Allah! We used to perform tawassul through the Prophet, (while he was alive), and now we will perform tawassul through the Prophets uncle, Abbas ibn Abd-al-Muttalib”. So saying, he commanded ‘Abbas to make a dua to Allah for rain, and indeed, Allah responded to his dua, and it rained in Madinah. [al-Bukhari 4/209]
Regarding this type of Tawassul there are some general rules that one should keep in mind:
1. A general rule is that a person should pray for himself. Just like he does his other acts of worship, and takes care of his own affairs in this world, so he should too make his own dua.
2. It could involve degrading oneself or humiliation by asking others too much.
3. No one feels more sincerity than the one making dua for his self. Sincerity cannot be expected from others when making dua for you, sincerity plays a key role in the acceptance of the dua, so it is important that you don’t rely heavily on others.
4. This type of tawassul may lead many people to stop making dua for themselves and to just rely on others to do it for them.
5. It may lead to arrogance on the part of the person being asked, for he may start to consider himself to be higher than his status.
6. It has not been reported than any of the major companions ever asked the Prophet (May the Peace and Blessings of Allah be upon him) to make Dua for them regarding a personal, wordly benefit that they desired. They would ask him to make Dua regarding a matter that was of benefit to all the Muslims (such as Umars request to the Prophet, to make dua to bless the Muslims with food when the army ran short of it during the Battle of Tabuk), or of a religious benefit (such as Abu Hurayrah asking the Prophet to make Dua to guide his mother to Islam, but there is no reported incident in which they came to the Prophet to ask for a personal, wordly benefit.
It has been reported that once a person came to Malik ibn Deenar (one of the famous scholars of his time). He asked Malik: “Make dua for me, as I am in severe circumstances”. Malik responded, “In that case, make Dua for yourself, as He is the One Who responds to the distressed who is in severe circumstances”.
In another incident, Tawus, one of the scholars of the Tabi’in, visited a sick person, who asked him: “O Tawus, please make dua for me”. Tawus replied: “Pray for yourself, for He is the One that responds to the one in distress”. [Al-Hamad, p.76]
These are the 6 ways found in the Qur’an and Sunnah by which tawassul can be done. If a person performs tawassul through any other way which has not been mentioned here then they risk falling into Shirk (making partners with Allah) or Bid’ah (Innovation in the Religion).