Requesting Someone to make Du`a & Tawassul (Ahadith 820 - 821)

Volume 2, Book 17, Number 820:
Narrated 'Abdullah bin Dinar:
My father said, "I heard Ibn 'Umar reciting the poetic verses of Abu Talib:
"And a white (person) (i.e. the Prophet) who is requested to pray for rain and who takes care of the orphans and is the guardian of widows."
Salim's father (Ibn 'Umar) said, "The following poetic verse occurred to my mind while I was looking at the face of the Prophet (p.b.u.h) while he was praying for rain. He did not get down till the rain water flowed profusely from every roof-gutter:
"And a white (person) who is requested to pray for rain and who takes care of the orphans and is the guardian of widows"... And these were the words of Abu Talib."
Volume 2, Book 17, Number 123:
Narrated Anas:
Whenever drought threatened them, 'Umar bin Al-Khattab, used to ask Al-Abbas bin 'Abdul Muttalib to invoke Allah for rain. He used to say, "O Allah! We used to ask our Prophet to invoke You for rain, and You would bless us with rain, and now we ask his uncle to invoke You for rain. O Allah ! Bless us with rain."* And so it would rain.
*It is of great importance to notice that it is permissible for one to request a living religious person to invoke Allah on his behalf; but if you ask Allah through a dead or an absent (person etc.) then it is not allowed. But it is absolutely forbidden to ask or request the dead for anything, it is regarded as Shirk (to worship others along with Allah).
Another thing is Tawassul. It means 'seeking to draw close'. Allah says in the Qur'an (interpretation of the meaning):
…[they] desire means of access to their Lord…” [al-Isra’ 17:57]
i.e. means of drawing close to Him.
There are two types of Tawassul:
  1. Correct Islamic Tawassul
    • through acts of worship which He loves and which please Him
    • by means of Allah's Names and Attributes
    • by means of faith and Tawheed
    • asking Allah by virtue of the best deeds that one has done
  2. Forbidden Tawassul or Bid`ah
    • by means of things He does not like and that do not please Him (words/deeds/beliefs). Example: calling on dead people, equating them with Allah in attributes.