A spiritual aspirant wrote his occassional routine of distributing food to the needy and forwarding its reward (esal e thawab) to the senior Sufis of the tariqa.
Hakim al-Umma Hadhrat Mawlana Ashraf ‘Ali Thanawi (Allah have mercy on him) replied,
“This is a reward earning act. However, in doing so the intention should not be to gain spiritual benefit (faiz) from the blessed souls of these pious individuals.”
Tarbiyet us Salik, volume 1, page 436
Most likely this is because it is against sincerity (ikhlas). It is just like giving a gift to someone with the intention that he will repay in kind or more.