The ASX stock Washington H. Soul Pattinson and Co. Ltd (ASX: SOL) has an excellent dividend record, which every passive income investor should know about.

Few businesses on the ASX have grown their payout for shareholders for at least 15 years in a row. This company is one of those impressive few.

Soul Patts started out as a pharmacy business more than 120 years ago, but it has turned into a large, diversified investment conglomerate.

Here's why I think it's a top idea for passive income investors.

Excellent diversification

Many ASX companies generate their earnings within one particular sector, such as banking, telecommunications, mining, or retailing.

Soul Patts is invested in many different sectors, including telecommunications, resources, financial services, swimming schools, building products, property, energy, and more.

Some of those ASX-listed investments include Brickworks Ltd (ASX: BKW), TPG Telecom Ltd (ASX: TPG), Tuas Ltd (ASX: TUA), New Corporation Ltd (ASX: NHC), NexGen Energy (Canada) CDI (ASX: NXG) and Pengana Capital Group Ltd (ASX: PCG).    

I think it's great that the company can invest anywhere it sees opportunities, as this can help it grow its passive income further.

For example, it has recently invested to increase its agricultural portfolio and has also taken full control of the electrification business Ampcontrol (which services the energy, infrastructure, and resources industries).

Defensive and growing cash flow

The Soul Patts portfolio generates a pleasing level of cash flow by paying dividends, distributions and interest into its bank account.

The various sectors that Soul Patts is invested in are typically defensive or at least largely uncorrelated to the general economy. With resilient (and growing) cash flow coming into the business, Soul Patts can then pay a resilient dividend for investors.

Growing dividend

With that cash flow, the Soul Patts board has increased the annual ordinary dividend it pays to shareholders every year since 2000. That's the best record on the ASX for consecutive years of dividend growth. It has boosted its dividend through events like the GFC, COVID-19, and inflation.

Another impressive passive income stat is that Soul Patts has paid a dividend every year since it was listed in 1903, which is pleasing to know shareholders are probably going to get a payment each year.

Soul Patts paid an annual dividend per share of 95 cents in FY24, which translates into a grossed-up dividend yield of around 4%, including franking credits. I'm expecting a bigger dividend in FY25 and beyond.